I had to look up incel.
I went to a fundraiser last night for an organization that assists victims of domestic violence. I learned that in the U.S., 1 in 3 women and 1 in 4 men are domestic violence survivors. I would not be surprised if incels were exposed to domestic violence at some point in their past. If you are experiencing domestic violence, I urge you to reach out for assistance. This link provides more statistics and information about domestic violence.
I wouldn't doubt it. You develop these unhealthy models of relationships when you aren't given examples of healthy models. Even bare neglect, extended over a long enough period of childhood, can lead to that kind of thinking. It's genuinely horrifying what kids can be exposed to early on that will absolutely fuck them up later in life.
Adult domestic abuse isn't as deeply scarring, but it can be just as severe. There's an aspect of psychological health that is obliterated when you can't even feel safe in your castle.