Tbf, some people want that. I prefer my instance which federates with anyone willing making you choose what to block yourself (aside from the reactionary instances that don’t like that we don’t block their enemy instances by default so they block ours, of course), but not just anyone can join my instance, so I can’t recommend that unless they qualify. If you have a better general instance I can recommend instead of .social I’ll definitely check it out!
Sure, but if they don’t know about it it isn’t influencing their choice. What I’m assuming is they’ll sign up for the one I tell them about and later if they have a reason to switch, like they find out “oh my instance blocks something I want to see” they’ll have learned enough to fix that on their own by virtue of using the thing teaching you about the thing. You seem to be ascribing some permanence to this choice, where there is none, you can simply make a new account, or another account and keep both, or 500 accounts if you’re a weirdo, it literally does not matter, there’s account migration. Furthermore there’s guides if you’re really struggling with the concept that pop up when you google “what is mastodon.” Like sure, my grandma couldn’t turn the computer on so she probably couldn’t figure it out, but it’s really not as hard as people make it out to be.