Most isekai readers: HOW IS A HAREM OKAY.!?!?
Real history: polygamy and harems for nobles was acceptable and prevalent throughout many cultures through history, including Japan and Europe. In fact it was sometimes seen socially poorly for a nobleman of a certain status and above not to have multiple women.
I swear people are so ignorant.
Yup. And there was no fights for succession, civil wars, or any kind of assassinations and infighting. Everything toootally worked out and they all lived happily ever after. /s
Obviously, harems and polygamy/polyamory can and do work but pretending they all work or didn't "work" at the sacrifice of rights of their partners (normally women, though I'm sure their are a few examples of men too) kind of sets things back for people genuinely wishing for those kind of relationships.
A relationship is hard work. Having multiple relationships is even greater work.
These manga don't care about all that and only care about selling a fantasy. That's it. Enjoy it. Love it but they aren't realistic. That's okay but you shouldn't be surprised when people say it.