In terms of safety, I don't think this is especially risky. Women are more likely to be assaulted or killed by a man they already know who's angry/ jealous/ controlling. Going on a handful of dates before having sex doesn't really give you any more insight into a person's character than a brief chat and you could argue that a 'date' is more likely to present a false impression of themselves (to try and get sex) than a man who already knows sex is on the cards.
There is a massive difference between going on a few dates and then having sex, or having sex as a transactional event in a hotel with a stranger.
A date isn't more likely to give a false impression to get sex as there are plenty of women like @Dockofthebaobun who are happy just to have sex! They don't need bother to 'pretend' to want more.
The former is that when you date you have some expectation of it developing into a relationship or even FWB, rather than a ONS. And you could have met the person's friends, colleagues, family etc. I'm not saying this is always the case, or the man isn't a nutter, but the odds of coming to harm are less.
And- being frank- the men OP has met so far don't care about her or want a relationship. They are getting sex, with no strings, they aren't paying for it, so from their point of view- why not go for it?
And the old chestnut that keeps cropping up about women being killed by men they know- yes, that's true. But this isn't just about murder or serious assault. They are unlikely. More being asked to do sexual things you don't want to do, so they become nasty but not so violent that there is evidence.
The fact is that OP has only had 4 encounters. The odds of anything nasty happening are low. But it's always a risk and the more she does it, the higher the risk. She's already found out the men don't care about her because of the no-condoms. For them it's probably no different to using a prostitute but without paying, or the stigma, (and the hope they can go condom-free.)
And before anyone wades in, I'm not saying the OP is 'like a prostitute'. Women are entitled to have sex with no strings as much as they want to. But some men have different views.