You can disagree without being rude. No one cares if you don't want kids/don't like kids.
that's like going on someone's photo thread of their child and then proclaiming that they don't like children. Children are messy and loud, why would you have them?
Or if I post a thread about my shelties and people come in 'Ew, I hate shelties. They're so stupid and loud and skittish. Why would you want one of those? totally not worth it.'
Neither of those are disagreeing, they're being rude imo. I hate when people are rude and when they are countered they call out that they just 'disagree'.