That's one perception, I suppose.
The other is that people assume there's something wrong, that you're lonely, or a visitor to the area.
You sit in a pub alone and you have no shortage of assholes thinking you have a sign up saying 'come over and annoy the shit out of me, will you?'.
If it's a evening, rather than afternoon, the likelihood increases 10 times over, with the added generous sprinkle of alcohol bravado.
Do you know the shit a women takes when she asks to be left alone, and some fella has had a load of beer?
How genuinely unnerving and disconcerting it can be? How sometimes, it gets to the point of insecurity and concern?
Ask those women, who don't like to be in a pub alone how many of them have been grabbed or groped. How many have had a drunken prick trying to corner her and kiss her. Ask them.
This is stuff that men in a pub alone have no experience of, I would imagine.
Women don't tend to sit alone in a bar, because they'd prefer not to put up with the shit.
Which is fair enough, I'd say.