Let me think, here's some:
1. It is unrealistic to think one person can fill every need (I know this, everyone says there is no such thing as the one).
2. It leads to a greater sense of fulfillment by loving more than one (I'm not too certain about this).
3. Allows for healthy amounts of alone time (something that can be discussed with proper communication in mono).
I understand how they view the world. But I also recognize that it's just not for me. But I just feel like I'm being pressured into doing it. I'm even questioning my parents relationship, and they're together for 26 years. I'm not saying one is better than another, but it just feels like my way is broken.