I think it's admirable that people want proof when the government is telling them something. Nobody really wants to swallow wholesale what somebody tells them constantly. Now the underlying reasons behind the lack of trust and where trust is actually placed is part of the problem, but probably a different subject from the one I'm going to tackle here.
The #1 problem with the evidence is when the public is actually qualified to effectively judge it or not. We saw the same thing four years ago in Ghouta. Some experts come out and say this. Some other experts come out and say something different. How is the public supposed to judge? You can see the same thing happening this time. Choose your own adventure:
You've got Ted Postol here:
http://www.globalresearch.ca/assessment-of-white-house-intelligence-report-about-nerve-agent-attack-in-khan-shaykhun-syria/5584867and here:
http://www.washingtonsblog.com/2017/04/addendum-dr-theodore-postols-assessment-white-house-report-syria-chemical-attack.htmland you have Dan Kazeta here:
https://www.bellingcat.com/resources/articles/2017/04/13/anatomy-sarin-bomb-explosion-part/Ted is a professor at MIT and an overall ordinance expert. He's been saying that the government, particularly the CIA, DOD, and POTUS, have been lying to the American people, since 2002, on a range of subjects.
Dan Kazeta is an NBC (nuclear/biological/chemical) warfare expert in Britain.
Ted claims that, by looking at the bomb fragments from the Khan Shaykun attack, you can surmise that the device used to deliver the agent was a pipe bomb or artillery shell, with a larger explosive placed on top of it to release the payload. He points to Al-Nusra being the culprit behind the attack, and says that the IC and DOD is lying, with or without POTUS being in on it.
Dan claims that the crater and bomb fragments are in line with an air delivered bomb load. Dan doesn't really call anybody out by name, but there are only three players in the area that are flying; 1)The Syrian government, 2) The Russians, 3) The United States.
There are other reports and open source investigation, like translated video, published flightpaths of Syrian attack fighters, and claimed eye-witness reports.
Both of Ted and Dan's analysis are based on looking at the impact crater and bomb debris. Both are considered experts, though with different histories.
Now, unless you also are trained in a high level of NBC warfare or a ordinance expert, you're going to have a hard time judging for yourself who is right and who is wrong. That doesn't stop thousands of laypersons from choosing their own adventure. But they're not judging the evidence using critical thinking, they're using confirmation bias to pick whichever presentation supports their pre-conceived notions and narrative. If you believe that the government and the IC is generally lying to you constantly, you can pick Ted's story. If you believe Assad is a general *censored* then you can believe Dan's story. It doesn't matter whose evidence is better or true, because you're generally incapable of making an actual assessment of the evidence.
All this of course brings us back full circle to the question of trust. Who do you trust? It's possible that you just don't trust the IC, because by nature they are secretive and involved in actions you don't approve of or because they've been proven wrong before. It's possible that you don't really trust anybody at all, and demand a certain level of evidence when the dentist tells you that you have a cavity, despite the obvious conflict of interest involved (the dentist makes more money if you have a cavity). But unless you have the technical no how and the sources of direct information, anybody could be fabricating evidence. The dentist could be holding up an x-ray of Jethro's teeth as far as you know. The doctor coming to cut off your leg due to sepsis could have the wrong one. It's not like it hasn't happened before.
So if you don't trust anybody at all, and demand evidence that you realize could be manufactured if necessary, you're generally going to be living in a state of paranoia. The alternative is for you to have to trust somebody, even if it isn't the IC. You may trust the media, or just particular members of the media. You can trust bloggers or outside experts like Ted or Dan. But all their evidence can be manufactured or countered. You're going to have to base your trust on something. It's not like the media or bloggers or experts havn't been wrong before. You're probably back to trusting whichever media sources or experts back up your general beliefs or narrative. You're back to confirmation bias.
I think it's understandable and right that people don't just take the IC or the FBIs word on everything. It's hard to trust somebody when they hold all the cards and refuse to show all of them to you. It's like playing Texas Hold'em with a guy who refuses to show his hole cards. "I have a full house, trust me". But their are checks placed on the system. The IC and FBI answer to the representative government of the US. The managers of the IC and FBI are nominated by the executive branch and confirmed by the representative branch. These are the people we vote for, presumably because we trust them. They presumably nominate people that are trustworthy and may also demand to see evidence that is restricted to the public.
Now, it could be you don't really trust the representative government either, or the IC. Even the POTUS has accused the IC of lying. And how is Cheetoh Jeezus or Representative Jethro supposed to know the difference between good evidence and bad? It's not like POTUS or Congress has a great deal of NBC weapons experts in their number.
The answer to that is that they really cannot, and the smart ones know that. That's why the smart ones have staff members, which they trust, who do have levels of expertise in some of these subjects, or they know where to go to find an expert that is trusted. This includes members of the NSC like the National Security Advisor, the Secretaries of Defense and Homeland Security, and all of their staffs. It's possible that they are all victims of confirmation bias as well, of course.
The main point is that there is a check against an IC or FBI that is fabricating evidence or lying to the representative government. They have the same interest that your doctor has for not lying to you. If your doctor lies to you, they can be sued and they will lose business. If the IC lies to the government, they can be fired and prosecuted as well. So the deep state evil wizard cabal in the basement at Langley have the same reasons to not lie as your doctor, dentist, or mechanic does. They want to keep their jobs, get promoted, keep their customers, and stay out of jail.
The final subject I'd like to cover is the standards of proof required by individuals for foreign policy decisions. Obviously we'd like to be as sure as possible when making decisions, especially when they involve us ending up killing people. But in most cases there will never be 100% rock solid "beyond a shadow of a doubt" level of evidence or proof. There will always be a chance of being wrong, no matter how slim. There will always be that 0.0001% chance of being wrong that someone relying on their confirmation bias can latch on to. Honestly, foreign intelligence usually don't reach that level. The best you can usually hope for is a "beyond a reasonable doubt" when it comes to these things.
That understandably bothers some people. But if you are going to wait for 100% beyond a shadow of a doubt, you are generally going to end up freezing your foreign policy, especially against players like Russia and Syria who have great propaganda machines. You're going to be incapable of timely action because you're never going to get that level of evidence you need to dispel all doubt. You're going to be frozen in indecision.
Unfortunately, foreign policy and other things cannot work this way. Even our justice system cannot work this way. Our domestic policy cannot work this way. Even science doesn't really work this way. Firefighters, police, soldiers, generals, surgeons, and all sorts of different necessary professions in the world cannot work this way.
Now, everybody is going to have different levels of sufficient proof for different things. There is nothing you can really do about that except that point out that at some point a decision must be made, because indecision and inaction effects the universe just as strongly as action does.
That's the end. Have a happy Easter.