Intriguing question.
I enjoy delving into the psychology.
It is not just a "man" way of seeing things, it happens for various reasons, but the main psychology behind it, is simply some people, are not educated or aware of the consequences, or they are too aware of the consequences.
Most common std's are as common as a cold, and easily treatable as a cold, thus some people won't mind taking the small risk, in order to have a sexual thrill. Even the bad std's like HIV don't show up for years, and a person can live a decent healthy life, so, there probably are people out there who simply don't care. On the other hand, some people just simply do not have the ability to look ahead into the future, and see themselves in the consequence, especially if there is the idea of sex near! But man oh man, once it happens to them, do they finally freak out!
Another view point of this, is that since in their world, std's are so "rare", they probably do honestly believe you are free of them, and they have nothing to worry about.
All i know is, this still happens, when you actually tell them you have std's.
I know a common situation, is the person ends up really truly caring about you, thus they are willing to take any possible risk.
Another more common situation, is that the person ends up really truly caring only about the lust, that they are willing to take any possible risk.
The whole thing about condoms being uncomfortable is true. For guys it feels quite horrible. It even feels uncomfortable for women at times.
A man would do anything to feel skin on skin. Even if it means sacrificing their life and getting HIV, in the moment of lust, no one ever thinks clearly.
It certainly does not mean they are bad guys. Even perfectly innocent virgin men can end up doing the same thing.
But, there is always the dangerous risk, the perhaps they don't care, because they already have an std - you should watch out for that!!! That is highly rare though, because everyone knows it's illegal to not tell before sex, but try to be on the safe side, and know who it is, you are having unprotected sex with. Make sure you can trust them first.
They are into the moment regardless of the consequences. Some women are that way too.
Maybe they're not too bright; maybe you picked a bunch of horndogs who just don't want to believe they can pick up an STD. Obviously they haven't been dating a group of very discriminating women.