not because there are better frontends out there

But there are, and have been for some time.

because he doesn't like the people in charge of steemit

That's putting it quite nicely. I'd argue that it's because the person (Justin Sun) and/or organization (TRON) who purchased SteemIT have been attempting a hostile takeover of the Steem blockchain for days now, referring to our consensus witnesses as "malicious hacker," and convincing 3 crypto exchanges to commit an unheard of act in using custodial stakes to overthrow a chain's governance system.

He says to #boycottsteemit

Correct, and I agree. Boycotts are one of the best voluntary, nonviolent ways to make change, requiring nothing more than taking personal responsibility.

It's not his decision to make.

Well, for him it is. For you, it's your decision. For me, it's mine. And we can each share our choice (or not) as we choose. And we can each adjust our decisions as we learn/experience more...

Using influence to censor a group of people is against decentralization.

He's not promoting any kind of censorship. He never said anyone should DDoS them, mute their accounts, delete their stake, fork away from them, or anything else. Simply stop being their products. Remember, SteemitInc's value is the number of users it has, its ad revenue from those users, and its Alexa ratings. You are their product, just like FedBook.

Voluntary, means you can say "no" if you want. You can choose not to interact with a person/group of persons if you choose, and you are more than free to share those choices with others.