I've been around the block of debating sites, and none of them have gotten so defensive when I've simply stating I'm approaching their claims skeptically.

This is no debating side. It a side for rational discourse about how to reason. As such we talk about the subject of how to reason. Not to defend something but because we care about how to reason and your particular way of reasoning.

I am aware of the philosophical meaning. If you don't mind, I'd prefer to just use regular terminology rather than your site-specific terminology.

You said that you don't understand what the website is about and people try to explain it to you. If you don't want to understand the local terminology you won't understand LW.

Also, it seems rather silly to me that your response to me effectively saying "I feel unwelcome"

You didn't you said people acted unwelcome. That's something different than saying you feel unwelcome even by conventional standards of language.