I saw someone make that statement about Torchwood's Owen Harper. They didn't like his Fragments backstory, the revelation that he had a fiancée who died, because it gave him a reason for being a jerk.
Now this struck me as odd, because for me, Owen's fiancée's death did not in anyway explain his particular brand of assholishness. In fact, the main reason that I dislike his Fragment backstory is that I struggle to see in S1 Owen the Owen we saw in the flashbacks in Fragments. It doesn't fit, for me. Sure, people can become unpleasant after the death of a loved one. But to go from being a devoted fiancée to the cynical, unloving and unlovable Owen of S1 is not explainable only by the death of a loved one. People who lose loved ones do not react that way from the death of a loved one alone. The equation of human nature is not as simple as: Bad thing happens to person -> person becomes unpleasant.
Which leads me back to the "jerk with no reason" description. Since every has reasons for their behavior, what is actually being said here? It seems the only thing that counts as a "reason" is suffering. Someone who is a jerk with a reason is someone who has suffered in a way that the fan deems sufficient to justify or explain - or possibly sanctify - his assholishness.
And that leaves me with kind of bad taste in my mouth.