I had an offer once, but I declined, as I had already had three beers and any further alcohol could compromise my judgment. Why, get me another beer, and I might have thought that following the guy home sounded like a good idea. I think that's why strangers buy each other drinks.
I've never bought a stranger a drink. Drinks at bars are freaking expensive (especially in Norway) and I'm not sure what kind of message that would send if I did.
"Here's a bribe for you to give me some attention"?
"I want to get you drunk so you'll do things with me you'd never do while sober"?
Buying drinks for (and receiving from) people I know, I have no problem with.
That one offer of a drink made me sufficiently uncomfortable that I think I might have declined even if I was nowhere near my limit. I'm perfectly capable of paying for my own drinks, thank you.