I work in the German film industry and know many professional editors. I always talk to them and ask if they use or have tried FCPX and usually they tell me that they have never tried it and they wouldn't go near it, as I was very curious about this "new way of editing". They usually tell me that they heard it's unprofessional and that they would never use it.
But I do know one editor, actually one of the best editors I know, he edits feature films for cinema and I recently worked with him. He loves FCPX and gets so excited when telling me about it. He says he has worked extensively with Avid and FCP7 and that he can do everything in FCPX and more and that he is so much faster and he enjoys it very much. But often he doesn't get the chance to use it. His last big project was on Avid and even though it's a great and strong system, he said it was painful and cumbersome to use once he's gotten used to FCPX.
I've asked him if there are any limitations of the system and he said, at the beginning, when it first came out, there were many and people still judge the application on these but almost all of them have been solved in updates. The one thing he mentioned is that you can't export OMF files for sound mastering but that there is a plug-in called X2Pro which solves this issue.
For his upcoming project, a big film for German cinema, he's fighting early on to be able to use FCPX as the editing system.
Perhaps some editors also feel threaten by it. Suddenly everybody can edit professionally easily. But good editors will always be needed, a good editor is one of the most important ingredients of a great film and can never be replaced by technology.
TL;DR
I feel like most editors reject FCPX out of closed mindedness and not wanting to learn something new. Those that open their minds to a new way of editing often find it to be a great experience and don't look back.