Since when have you ever known a board to convene a shareholder's meeting before making a decision? The only time they even put anything out to a vote is when required by law. They are the agents of the shareholders, and when the shareholders don't like their decisions, a stakeholder with a significant position mounts a challenge to board elections.
As for the poison pills, they aren't uncommon.
In 2012, Netflix was caught off guard. Carl Icahn, a well-known activist investor, acquired over 10% of Netflix’s shares without the approval of the company’s board. Activist investors typically acquire large stakes in companies with the intention of effecting changes in its corporate policies or management. In response to his threatened intervention in the company’s affairs, Netflix issued a shareholder rights plan. Their measures enabled the company to flood the market with new shares if a corporate raider acquired a large amount of Netflix shares. This use of poison pills was successful and Mr. Icahn’s stake in Netflix was significantly reduced.
More recently, in 2016, Pier 1 Imports adopted a poison pill plan to steer away a hostile acquirer. Pier 1 implemented a shareholder rights plan shortly after Alden Global Capital, a hedge fund, acquired a 9.5% stake in the company. The poison pill gave all holders of common stock the right to buy a fraction of junior preferred stock at a discounted price. The plan that Pier 1 Imports adopted made the voting rights of preferred stockholders and common stockholders similar to each other. In effect, this diluted the control rights a large shareholder could exert over the company.
Activist investors don't automatically represent the shareholder's interests. I suspect the main argument, Fenring, is that if you were (or are) a twitter investor, you think Musk would do a better job than current management. But other than "bring conservatives back", I don't see any evidence that Musk has plans that would yield better returns. He's bought them out now, so we'll never know. As a private company, he can lose money like a leaky bathtub and never has to disclose it? So he can run the company as part of his moral crusade, and no one will know the result.
He wants Twitter's algorithm for prioritizing tweets to be public and objects to giving too much power on the service to corporations that advertise.
That would make me nervous as an investor. That's how twitter makes revenue. If he follows through on plans that would make the platform less valuable to advertisers, I'm going to go out on a limb and say they won't pay the same amount to place ads.