Why do some people think that monogamy is unhealthy?

I’ve noticed a pattern lately of people responding to the idea of a monogamous relationship as “unhealthy” and “you must be too insecure for an open relationship”?

Just finished watching a YouTube video on open relationships, and the entire comment section was filled with people bashing others for being hesitant to the idea of sharing your lover.

What does jealousy have to do with it at all? I’m just curious if anyone has an answer to this because I’ve always wanted to know.

For me, I could never be in an open relationship. I give so much of myself to people when I love or care about them and I just would have nothing emotionally left to give to yet another person besides the one who I first chose. My energy, feelings, peace, body, etc are things that I can’t just give out voluntarily to multiple people. And the thought of voluntarily opening the door for others to enter into my monogamous relationship leaves greater room for a change of mind in who I love or who my partner might start loving more than me, which is not the outcome that I’m striving for. I don’t believe in one soulmate so I do believe there are multiple people that you could connect with and love if you look for them, and that all just sounds so exhausting to me.

Also, why is it deemed unhealthy to be territorial (*to a certain extent!!) in a relationship? If you and another human being have decided you want to be together, how is it a bad thing to not want to share them?

Interested in hearing some different views and opinions that will help me understand!