There are men of all kinds out there. You just have to cast a wider net - in addition to Internet, meet as many people in real life as you can, since you never know who might introduce you to a great guy some day. Go to all the parties, munches, etc. you can, even if you don't think there will be any interesting guys there. The more you spread out your social contacts, the more likely that you'll meet someone.
It might not hurt to examine your criteria, too. Do you have height restrictions? Do you only tend to be attracted to aggressive men (in the vanilla sense)? What are some types of guys that you don't usually look at, but who might turn out to be hidden gems (ex. shy guys)?
Most of my male friends are pretty obsessive about STD prevention, but I have known some who aren't. In my experience, those men have never really grown up and learned to temper their instincts with reason. The same goes for women, though - there are a LOT of women out there who don't insist on protection, and even some who ask that a man not use a condom. I have even heard swingers - who are at high risk of STD exposure - claim that other swingers are "safe" and that AIDS is not present in the swinging community.
I have never had sex (oral, anal, or vaginal) with someone without first discussing sexual histories and getting a full range of STD tests (so no sex on the first date). Even with that, I use a condom every time, including oral sex. I have no desire to pick up a disease (particularly an incurable or fatal one), so I try to be as safe as possible.
You may have stopped receiving responses to your ad because you used the phrase "friends first." The phrase "let's just be friends" carries a lot of negative emotions for many men, because women have used that phrase with them as a euphemism for "I don't find you attractive." Though "friends first" would imply something different for me, there are probably a lot of men out there who would see that combined with "no casual sex" and assume that it means that you are opposed to sex before marriage, or that you would make them wait a really, really long time before having sex.
That isn't to say that you shouldn't have those two phrases in there, of course. They may even be acting as a good weed-out filter for you. My advice would be to remain patient and pursue other avenues.