I've seen so many poly people having the "needing deep connections and trust", as well as the "dating only one person prevents you from forming different bonds and relationships with other people in a romantic way and missing that is sad" arguments against monogamy. At the same time, many poly people I know or I've heard about (keep in mind that don't know every single poly person on earth) actually lack proprer friendships, or have no genuine friends at all.
A poly person I knew considered their acquitances (ie, persons they tolerated, liked to spend some time with but not too many of it, worked with) as their friends. And they told me they had romantic feelings whenever the connection was stronger than that : being able to have deep conversations, sharing interests, and the other person being a safe space. Which, to me at least, is the basis of friendship.
And this is sad to see, as someone who has several healthy, deep friendships, and circle of friends which I can confide in without having to mask, people lowering their standards like that.
I had one ex which cheated on me on the pretext that she was polyam. Her way of seeing her friendship was that she had one main "friend" in her life, which she spent all her time with, and this relationship was very ambiguous as well. I was in this position, as her partner later, and she was jealous whenever I interacted with friends (and I meant in a normal way ie talking and spend time with, not flirting or trying to date them or anything gross like that). But at the same time, she blamed me when I told her kissing another guy was cheating, on the pretext that she was poly and couldn't repress her needs. She mixed everything up.
And I saw many poly people being like that : friendship and love are close things for them, or even sometimes, the same thing alltogether. They don't seem to have the same limits to what's everything supposed to be differenciated by.
And I mean, in the end, they're adults and choose whatever fits them most, I guess. But knowing that there's a big chance they're missing the point of having genuine and amazing friendships and a partner who truly loves them, and instead, choose to share what's not shareable (in my opinion) ie their lover, and have these weird, unhealthy dynamics where their friends are the people who share their partner with them...
Instead, they choose to have shallow friendships, and involve themselves systematically in romantic situationships which will inevitably break at some point. They're thinking that this lifestyle will give them opportunities to build stronger relationships, but at the end, they're making them more fragile, more difficult, more prone to drama. And they're bringing themselves closer to isolation, which is truly depressing. Both for them and to an exterior point of view.
And truly, I think they're missing out something amazing. Hoping to see some of them think about that and change their ways instead of denying their, and their loved one's needs.