What's depressing about it? Sex is a good time. Why would you turn it down if it's being offerred up? If the act of sex with this person would mean they would be cheating on someone else or something like that then THAT'S depressing to know.
But what's wrong? If a girl WERE to come out of a room naked and offer up sex, I think that's a pretty clear indication that it's a mutual wanting of sex and there's nothing wrong or depressing about that.
It doesn't mean that all this time we WANTED sex with them. If we were such good friends to begin with without sex then it's pretty obvious that we don't want them for sex. Cause if we did want them for sex, we wouldn't be friends without having gotten any after such a period of time. But why turn down something that's mutually offerred up and would be a good time?
Lemme take YOUR quote and modify it and see if it still holds true....
have a challenge for all of you girls who still doubt [that all guys want sex/money/a car/a computer/nice clothes/a watch/a free dinner/etc. etc.]. Pick a guy that you think is your friend. Then ask yourself this question: If you were both alone at his place one night, and you excused yourself to the bathroom and came out naked/with a twenty/holding car keys/holding a monitor/with designer jeans/holding a fossil blue watch/with a gift certificate to Red Lobster/etc. etc. and asked him to have [if he wanted it] would he:
1. Tell you he doesn't want to risk the beautiful friendship you have created with messy ... entanglements.
2. Comply.
I think in ANY case, the guy would comply. It's not SEX we're after. But who in their right mind would turn down something that they think is nice or fun or would basically make them happy if the other person were willingly offering it?