That's all dependent on where you live. Maybe where you live that's socially acceptable?
Where I live that's not socially acceptable. It's considered rude and offensive to approach strangers in public spaces unless you have a prior social connection. Even the dog park is like that here.
The only place where it would be acceptable is at these socialization events, and those are often highly structured, like those events where you have to ask people questions on index cards in a weird attempt to force intimacy. 'skip the small talk' type of shit.