Re: OK but why is trendy bad?
Ditto Akua Topaz. I also want to ask you, do you like the names Bertha or Mildred? These were both wildly trendy names in their day (Mildred peaked at #6!). Now most consider them horrid old lady names and very unusable. They are so tied to a particular generation that they're, well, ugly to the modern ear. And poor Grandma Mildred has people thinking "yeesh, what an ugly name". I don't want my child's name to be considered ugly or frumpy at any point in his or her life. And yes, I believe that Madison will one day be Mildred. It may not sound ugly right now (well, at least to some), but styles will change and different sounds will be considered beautiful or ugly.
My other probably with trendy names is that many (though not all) are devoid of much meaning. I want my child to have a name that has some history, that has some namesakes tied to it, that isn't just a collection of sounds. This may make me a "name snob," but so be it. I suppose that's more of a personal taste thing than being right or wrong.