He most likely hates it because everyone told him too. One of the more common reasons people hate the M9 is the pistol grip is rather large. The M9 is a fine pistol. It is quite durable. Most soldiers, sailors, Airmen, and Marines beat up all the equipment they are given. Also in order to get a government contract the M9 had to go through more tests than most pistols on the market today.
I agree with this 100%. Every time I hear someone bashing the M9 and saying how "crappy" it is I just ask them why they think that... The majority of them have no valid reason. The only malfunctions that I've encountered were due to mags that were a couple thousand years old and needed to be replaced.