People who are insecure tend to not tell others actually, they keep it bottled in their own heads. They constantly put down others in fear that they would be put down as well, or tend to degrade others to make themselves feel higher of themselves. They try to make the ways of others seem odd and peculiar to lower them. Sounds like you. People don't just admit they're insecure, they reject the idea they're insecure.
Well having high self esteem is as seeing yourself better than others, so yes you would degrade others or their ways. It's how high self esteem works. I don't see myself as less superior than others around me. And yes I've seen people admit they're insecure, on the internet more than in real life because you're more anonymous here. If I say I have low self esteem, I'd be lying to myself, if I say I have high self esteem, you'd think I'm boasting.