>shouldn't it be within the user's purview to decide what to allow and what not?

Imagine it this way: The local supermarket is selling a product which claims to be food but actually contains a highly toxic poison. And then someone justifies it still being allowed because it's still up to the buyer to choose to buy and consume it. It's on the user, the should be responsible to look for trusted brands that do not disguise poison as food or they could take it down to their local lab to test it for toxicity before consuming it.

It's obviously completely absurd to expect the user to protect themselves from malice like this which is rampant on browser extension stores.