>Just because your monogamous friends are happy and fulfilled doesn't mean your slutty friends would be happy if they lived the same way.
This isn't backed up by research which seems to suggest that the more sexual partners you have, the worse your relationships are in practically every dimension.
This is an area where it's very difficult to show cause and effect (since you can't exactly do a randomized controlled trial) so I would be skeptical about drawing conclusions that lowered relationship quality is caused by having more partners.
This isn't backed up by research which seems to suggest that the more sexual partners you have, the worse your relationships are in practically every dimension.