For all of the talk about how "monogamy is unnatural," why do the people who advocate for serial monogamy continually throughout the lifespan or polyamory not discuss the many downsides of their chosen lifestyles?

Point #1: Breakups are horrible, and promote suicidality. They are at least as unnatural as monogamy because we as humans evolved to preserve social bonds, and breakups activate the same part of your brain that processes physical pain: https://www.google.com/amp/s/www.insider.com/why-do-breakups-hurt-so-much-2019-2%3famp. Breakups cause cortisol, the stress hormone, to spike through the roof, and can even damage your heart.

They may be a necessary evil for most of us while on the road to finding a compatible life partner and successful relationship, but they should be experienced as rarely as possible and avoided as much as possible for the reasons that they are horrible, painful, and wholly unnatural.

Furthermore, human beings evolved to fall in love during the act of sex and particularly when having sex repeatedly with the same person. The three stages of love are lust (what first attracts you to a prospective individual), infatuation, and finally, attachment.

Point #2: Polyamory promoters tout the virtues of the second stage of love, the infatuation stage, characterized by "new relationship energy," or NRE. Let's talk about why this is an impractical way to go through life, and the many downsides of NRE. First of all, NRE/infatuation is ruled by dopamine. Why would anyone want to spend their life on this hedonic treadmill perpetually chasing the dopamine high of a new relationship? Do you just keep adding new partners indefinitely when your brain acclimates to the last one and the novelty wears off until you have 50 boyfriends and girlfriends? At some point you will have to deal with a breakup or several. This is bad (see point #1).

Point #3: If you're in the kind of relationship that is "open," where the sexual partners you have on the side are intended to be casual and falling in love with them is to be avoided, how do you control something like that? If you do involuntarily experience the sensation of falling in love with your partner on the side that is supposed to be casual, which, again, your body is designed to do when you have sex with someone - this is natural - you then have to deal with the many downsides of dopamine-fuelled NRE; unwanted persistent and obsessive thoughts about this person that make it hard to focus on your day-to-day life and your legitimate partner, unwanted mate-guarding instincts which you are impotent to do anything about to actually guard your mate, and, once again, when the inevitable breakup happens, the horrible feelings of withdrawal which will ensue and the subsequent depression, because breakups are unnatural.

Then of course there are also the practical concerns about communicable diseases (STDS such as herpes and crabs, deadly respiratory ailments during pandemics, etc.) that naturally arise as risks during any exchange of bodily fluids. Again, partner changing should be viewed as a necessary evil in the face of incompatibility on the road to finding a permanent partner, and nothing more.

All of this is inconducive to stability, optimal productivity, or, I would argue, long-term happiness. These feelings and sensations can be best described as drama.

Those who promote nonmonogamy, why don't you just concede that you embrace and love to invite drama into your life?