So what do you suppose the actual hetero-on-gay violence is? Especially if you take out clear cases of self defense?
In a man/man or woman/woman "arrangement," the odds are virtually equal, and conflicts are more likely to be prolonged and stalemated due to like forces unwilling to budge. This can, and usually does, escalate into extremely violent resolutions.
It's no surprise that these equally matched constructs fail at a much higher rate than natural man/woman unions.