What do you think the point of Facebook is if not to look up people socially? That's literally what a 'face book' was originally for.

Also with the number of fake profiles and lying that goes on these services it's worth checking just to make sure they're a real person. Otherwise you ask some more questions or just act cautiously until you know they're a normal person. (e.g. Not a con-artist or scammer. etc.)

You generally prefer the other person not knowing you "cared" that much, but it's a simple vetting trick.

Fear of everything you do in private being creepy is just a self-limiting belief.

Digging for bikini pics isn't part of the process here.

As a woman, it's a basic safety protocol to at least check that a man doesn't appear obviously crazy before going out with him.

Same goes for men too...

A man is not usually at risk of any physical danger, though.

I'm pretty crazy but you'd never know it by looking at me.

I specifically say I’m not crazy on my profile.

Is having a facebook account an important place to start when trying to establish the appearance of sanity? Asking for a friend...

I'm surprised you're being downvoted, I agree with you. I'm not even sure how you would do this, as Tinder Bumble et al don't show surname. Search by given name and job / university? Not everyone shows those, and even if they do, I agree it's weird to stalk someone's info on FB just by finding their dating profile.

It's like picking your nose in private. You can raise a stink in public about how you'd never do it with fake disgust, but I'm sure you do it.

I don't think it's any less weird to meet up in person with someone after just seeing 3-5 pictures of them and a vapid bio. Looking at the Facebook profile can give you a sense of how they conduct themselves and whether they're crazy. Like if their wall is dedicated to some MLM scheme and they get in fights with their friends/family. Or whether their Tinder pictures are from 5 years and 100 lbs ago.

If you think it's weird, then I'm not convinced you've used Tinder enough to escalate it into a date. If you did, you'd know that having one mutual friend in common makes it easy to hunt them down and even if you don't, Tinder gives you enough info to anyways unless they have their privacy settings jacked up.