We just discussed this peripherally in another thread, so I'll restate my position here. The traditional arguments against a high number of sexual partners -- that it makes one "impure" or that it is a sin against God -- are obviously silly or are reliant on religious convictions that not all of share. As such, those are not reasonable arguments .
However, saying that a large number of sexual partners is "not unethical" is not the same as saying "it's a good thing." Watching lots of TV is not something many of us would say is unethical, but we wouldn't exactly say it's great thing to do, or that it's a highly productive use of your time.
In other words, any complaints I have about promiscuity are comparatively light, and are certainly not based in traditional moral values, which, again, seem illogical to me. I tend to be drawn to aggressive, driven people who are highly accomplished, and thus don't have a lot of time to spend playing video games, or watching lots of TV, or seeking out lots of sexual partners. This is not an absolute rule and of course no person is a machine who spends absolutely no time on ephemeral pleasures -- I certainly don't exclude myself from that, either -- but people who spend a relatively large amount of time focusing on immediate pleasure are rarely going to appeal to me, and this applies to both genders and to romantic and non-romantic relationships.