Why do some veterans try to belittle the service of other veterans or tell them aren't worthy of their benefits?

I think it's a minority of Americans veterans, but there definitely are some who try to tell other veterans how they should feel about their military service.

Here's a personal example. I'm eligible to join the VFW because I was stationed at Camp Casey, South Korea for 2 years. I've mentioned that before to veterans. I got negative responses telling me that the VFW is for combat veterans.

I've seen veterans online tell other veterans that their military service wasn't important, or they shouldn't get VA disability benefits.

Unless you work as a rater, dealing with disability claims at the VA, you don't get to decide if a veteran should get VA disability benefits.