People are afraid to be disliked for raising concerns. But think of it like this: Would you not yell at your taxi driver to watch out for a dangerous oncoming vehicle, just because the driver might be offended by your volume? In any case, Jayson Demers writes for Inc. about how to raise concerns without sounding negative.
He says to get specific about the things to which you object and be objective about it. That makes it easier to recommend some possible solutions to the problem, which you should have ready to go at the same time you raise the issue. Just make sure to pick an appropriate, non-disruptive time to broach the subject, and do temper the conversation by discussing positive aspects of the problem. Even if the issue does not ultimately get resolved the way you would like, at least it is on record that you shared your concerns. For more, you can view the full article here: http://www.inc.com/jayson-demers/how-to-voice-concerns-without-seeming-negative.html