Believe me, after years of running forums on the internet, people can get behind just about any ideology where belief is a factor, (not just religion) and defend it to the death.
It really depends on the person. Some invest a lot of their selves into their beliefs, and any attack on the belief is seen as a personal attack. As humans, we're unable to be totally subjective about anything, but some are less able than others.
It's just one of those things about the way we're emotionally constructed that gets easily distorted. But, the more we're able to see the other person's point of view, the more rational we try to be, and the more we TRY to be objective about our own thinking the less combative we will be.
One of the first things one learns in cognitive behavioral therapy, a therapy designed to root out faulty thinking that lead to depression, one thing you have to rid yourself of is this notion that to be lovable, everyone must agree with you. (Ironically, this "faulty thinking" check list was once printed in an Awake article about depression.)
I really think that's why so many Witnesses suffer from depression. They think everyone must agree 100% on everything to be loved by God and by each other. That's not only unrealistic it's CRAZY.
Humans naturally differ in opinion because we are all unique. Witnesses don't agree nearly as much as they pretend to about belief or anything else. They just feel compelled to pretend that they have this amazing (and virtually impossible) unity.
A Catholic can say "I disagree with the Pope about birth control" and not have to worry that he won't be thought a Catholic for thinking and saying that. A Baptist can say, "I can drink beer if I want!" and not have to worry about not being able to go to the Baptist church and be shunned for everyone knowing that.
Most mainstreams religions have the good sense, for the most part, to be tolerant of the differences of belief and behavior in their membership, even if it's outright disagreement with doctrine.
Notice that religions like Islamic fundamentalism are railed against more and more for NOT being tolerant of individuality. People think more and more that it's WRONG to be this punishing of dissent and individual freedom. Because deep down we all know how normal it is, and how abnormal to suppress it.
Witnesses have to deal with the same intolerance of individuality as other fundamentalist or high control groups and it makes them extremely defensive about their beliefs. They have to deny so much of themselves to adhere to it, they have to convince themselves it's worth the sacrifice.
They may not be violent about it (they can be, though) but it's pretty much the same mentality that causes a man to strap a bomb to himself and die in the name of Allah as it is for a Witness to refuse blood and thus believes he dies faithful to Jehovah.
Better and so much more emotionally healthy to just accept that people have varying experiences, personalities, beliefs and ideas, and to agree to respect that.
Groups, parties, religions can only define you to an extent...when they define all or most of you, the extremism begins.