Why are Seinfeld fans so insecure about the success of Friends?

Because people make it sound like Friends is some top tier comedy. I never watched Friends, but I get the appeal, but this wasn't a smart knee-slapping comedy.

Sounds like a dick measuring contest to be honest.. Both shows were incredibly successful, however, it can be debated that the show FRIENDS was a ripoff of SEINFELD

Is it not possible to like both?

Never knew there was a Seinfeld v Friends rivalry, most people I know have enjoyed both and probably prefer one over the other but not with any kind of beef.

I like the disingenuous wording you employ. No Seinfeld fan is "insecure" about Friends. Friends is a more vapid, easy-going sitcom. People learning to speak English love it because the language is so simple they can actually understand the jokes. Seinfeld is a MUCH MORE complex sitcom (particularly the seasons Larry David was involved). The humor, while often silly, is somehow more sophisticated than Friends. While Friends operates like a soap opera with a laugh track, Seinfeld is almost an anti-sitcom in that it refuses to be warm and comforting (though because the humor is so good, the jokes never get old, therefore the humor itself is a form of comfort upon repeat viewings).

Insecure about what? Both shows have their fans, were hugely successful in the their original run, and are still popular to this day.

They both get in a tizzy when you point out how superior Home Improvement is.

The word "insecure" doesn't make sense in the context of your post. Are you trying to say that Seinfeld fans unlock their doors or tell their bodyguard to leave when someone says that Friends is better or more popular? Or are you just doling out psychobabble?