It's mostly nonsense. If you think a tile pattern looks bad, don't get one. If you like it, get it. The leveling issue is not as great as they say--if you are using a beaded liner, the pattern will follow the bead.

Sure, some of the patterns are nice, and some are hideous. That's true of tile, carpet, curtains, EVERYTHING...There's no accounting for taste.

However, I have found that when a contractor recommends against something you want you have two good choices and one bad choice:\
The good:
Follow his advice.
Find a contractor experienced in doing what you want.

The bad:
Make him do it anyway. In 9 out of 10 jobs, you'll be sorry.

Been there, done that.