Indeed. When one wrap his entire personality around an opinion - as well as around the idea of converting everyone else to that opinion - he has no room for emotional leeway should someone contradict him. Instead of being able to take a non-congruent comment as, "I disagree," they are forced to take it as "I think you are a complete idiot." Low self esteem = low quality debates.
Hence, the "trolls" you find prowling around this site are, more often than not, trying to defend issues that are not only important to them, but have, in a sense, become them (i.e., political parties, race, religion, etc.)
Those are my thoughts, anyway.