@adam-
Two things can exist at once, even if they look like they oppose each other from the outset.
You need publicity to bring attention to your idea, and sadly being contrarian is a low hanging way to effectively do that.
You can care about decentralization and understand that in order to bring the concept to a larger demographic you have to engage on a centralized platform to inform them.
Sending a message about decentralization within a decentalized app is tantamount to saying something within an echo chamber.
That audience is already on board with that concept, which is why they are already there.
To @matthew's point, these purity tests definitely do more to alienate people than inform. People are their own worst enemies when they take this approach.
To @depressivehacks point, the platform is not a monolith. If you want your message to have reach beyond your own demographic, then for better or worse, you say it wherever you feel it needs to be heard