I think that you should just ignore them. People that make comments like that are just being ingnorant, immature and are looking for an argument.

Perhaps its worth thinking more about the enjoyment you get from playing rather than technique. I play french horn as well as flute - and usually when people hear me play flute they ask why I prefer to play french horn! The fact that horn parts are normally much less melodic doesn't mean that they are less rewarding to play.

"that I have had several people say that playing the flute is easy because all you do is press buttons and you dont have to move your lips.."

As you already know, they don't know what they are talking about. Each type of musical instrument has it's own set of probelms and it's own unique type of tone quality. They are all to be enjoyed.

That being written, the problem with the cornet and trumpet is that the bell points the wrong way. It should curve back towards the players head like the French Horn so that they can hear how loud and bad they are actually sounding.

every instrument is difficult...