I'm the same way with you, but that's also why I don't go to coffee shops to study/think. I'm simplifying and assuming a lot here, but: Why would you go out to a place like that for "alone time"?
I kind of like the background noise for some reason. It wouldn't surprise me if our brains evolved to be most relaxedness and free from other worries when surrounded by other humans, making it a good setting for doing some studying or whatever.
I can see that. I personally prefer music, but I've definitely heard of people turning on the tv for "background chatter" when they live alone.
My point is though: By putting yourself in a public setting, you are more likely to be approached. I don't want to say "asking to be approached", but I'm not sure how else to articulate my thought |:)
I wouldn't be shocked if a stranger approached me in a coffee-shop. I would be if they approached me in my home!
Here's the thing, I shouldn't expect to be met with other people's rudeness. That's not my fault. They are the ones that are rude. The exact attitude you're displaying is exactly what you are struggling to avoid saying.
I'm not shocked if a stranger approaches me; I consider them unable to recognize the social situation and they are being rude. I also grew up in the city, where the socially polite thing to do in most public situations is to leave people alone.
I go to coffee shops because I like the laid back atmosphere of many of them. I also like the smell of coffee and people watching.