I believe that yes, males and females can be just friends but my experience with it definately points in another direction, with other guys vs my SO that is. I've never been one to keep a lot of friends of the opposit sex, or just friends for that matter but I have had some without it being anymore of a friendship though ( but lots of guys can't be just friends, some even says so them self)
My SO is a very attractive woman of both looks and personality and unfortunately for me, lots of other guys seem to agree.
It has happened, on multiple occasions that she had a male friend which turned out not to be a friend. Sometimes they tried to have sex with her, other times they genuinely fell in love with her (and the fact that they knew she has been with me for over 5 years didn't seem to stop their advances at all).
To be honest, I would much rather that she didn't have friends of the opposit sex. I see them all as potential threats and if the past is to be any indication, then I would have to say that it's with good reason too.
At the same time, one has to ask one self, even when offered, would something happen? I mean, let's face the facts here. ANY woman of above average on the sexy scale would be able to get laid in a matter of minuts if she really wanted to. Hell, she could just go right out on the street and ask a random dude.
So one has to make up his mind on whether or not the trust is really there. If it's not, then the person either isn't right for you or you are not mature enough for a relationship.
And I trust my SO, I really do. But I still get frustrated about it. Not because I fear that she will cheat but because I fear that at some point, one of these "friends" won't take a no for an answer or that she'll eventually meet someone that she develops strong feelings for - both would be absolutely devastating to me so I do have some anxiety about her having male friends. Other than that, I also hate it then other guys have some kind of attraction towards her, if I were a little more mature in this apartment, then I would probably take it as a compliment but it makes me kind of want to puke instead. I definately has some growing to do.