I used to have a roommate who could go out for eggs, milk, and a quick romp in the sack with a stranger. I would say she didn't care much about the person involved... most of the time. There were a few, though, whom she kept around(both knowing it wasn't headed for a relationship), and was quite fond of them. So, I can't say she always had the same response.
When I worked, I had a revolving door of coworkers who were in their early 20s(the place recruited from a local campus). I would say I found mixed attitudes there, too. Though there were exceptions, I'd say most looked at casual sex as just part of a good time, and behaved overall respectably to their temporary bedfellows.
I do think there's some expectation from men(from other men) to brag about numbers while they're in their early years, whether there's truth in it or not. I remember talking to an acquaintance about someone we both knew. He told me "So and so says you took their virginity when you were both young. I would have never expected that!" to which I told him... "Well, I'm honored he chose me for his first time, but you let him know for me that it has to be more than him and his hand to count!"
While it could be said 'number bragging' is dehumanizing, I think a lot of it is just bull manure that the immature engage in.
There was a lot of bull manure of that variety in my small town during high school too. Life of a pre-adult. But some girls would call them out on it, which was always good for a laugh at the expense of the braggart.