Wow. <shakes head> I had to read that three times to make sure I didn't miss something the first time. I couldn't disagree more.
A great many people live a non-monogamous life in a very healthy way, and share the same love, respect, acceptance, trust, support, etc. that monogamous couples share. I would even make the point that (due to the circumstances) the trust factor is often even higher than that of many monogamous couples. Of course, that's an opinion and not provable.

And the non-monogamy quite often helps make the sex incredible between the couple.
I confess that I'm not tracking what you mean here, but I have a feeling I'm going to disagree with it.
I would say that opening the relationship
can be complicated but it doesn't have to be. If you have two people committed to one another, it can simply be a few hours of yummy fun, then it's over and we go back to our lives. I do agree that a couple playing with the same partner (or partners) multiple times in a short period of time, can run the risk of someone in the group "getting the feels". This is typically solved by only meeting up with the same person/people no more than 3-4 times a year.