It's completely relative. Micro-transactions can be fine. They can also be horribly destructive. It all depends on how they are used. Aesthetic add-ons and resources that you can already get in-game are fine. In that regard, the only impact they carry is to appearance and to save time and effort. Personally, I'll ignore these things, but I don't mind that they exist.
The problem will come with any game, and this will happen eventually, that endeavors to force players into purchasing items to compete and/or advance. At that point, it will be a broken model for anyone who feels that they've paid for a full experience when they bought the game. I'm not saying all games will do this, or even most, but it will happen sooner or later.
I'm not going to "boycott" games for having micro-transactions but I certainly will if I learn that a particular game is cheating customers who don't fork over additional dollars.
