Being monogamous with a cheating partner is...not so great at it. Their tolerance for risky behavior is obviously high, and they're already showing a lack of care for any consequences by stepping out. Yes, I know, "my partner would never be unfaithful," and I hope that's the case for everyone reading this. But it's a common enough occurrence that we all know someone who it's happened to.
That's not a case of real monogamy. We could call it "attempted monogamy" maybe. Cheating partners often want to keep their original relationships intact and as such don't take extreme risks. They probably aren't sleeping with other people as often as a poly person would, and the type of person they sleep with is likely less promiscuous than a poly person.
It seems pretty clear to me that STD risks are lower for those in nominally monogamous relationships, even if there is always some risk of cheating. Redefining the cheating as acceptable behavior (that is, redefining the relationship as poly) is not solving any STD problems. It might if you absolutely cannot trust your partner to be remotely monogamous, but you do want to stay with them, and you do trust them to tell you who they're sleeping with, AND you can effectively use that information to reduce your own risks. For me, I just don't want to be with someone who does not think I'm enough.
I never said it's a mystery. I'm saying that monogamy is much safer than nonmonogamy in terms of STD risk. These risks are not negligible. Look at how many people have herpes for example.
>I actually invited more strangers into my home back when I was monogamous, honestly, but I'm not sure what that has to do with polyamory.
You don't have to sleep with strangers to be poly, it is true. But I think most people who are in fact sleep with strangers and others who might profess to be poly yet secretly have a lot of jealousy.
>Monogamous people lose their partners all the time, have you seen the divorce rates?
They lose them less than poly people. That's the point.
>None of what you are suggesting matches my experience.
Since many of the downsides I've explained are in terms of relative risks, one instance of good luck does not disprove it. I also think it's common sense that having more partners makes life complicated and introduces more significant risks. Hell, even one partner can wreck your life. More than one, especially the type of people who partake in such deviant and risky behavior, is just asking for trouble.
The negative view of monogamy that these people convey is an attempt to justify their lifestyle to people who don't like it, or to recruit more people to their lifestyle. One could argue that both monogamy and nonmonogamy have selfish aspects, but monogamy has proven more successful as a strategy for human society. Of course polyamorous people would debate that with you, but the disadvantages of polyamory are so obvious that it isn't easy to justify.