I answered a similiar question in referance to a question relating to God and religion the other night... for most, it boils down to this: Anytime you ask a question about a controversial or opinion oriented subject... we all want one (or both) of two things:
a) to have others who agree with our opinions reaffirm those opinions and make us feel better about our own beliefs.
b) to have others disagree with our opinions so we can pick a fight and "prove" them wrong... typically using more opinion oriented statements... an exercise in futility at best.
Now... to differentiate from what I've just said, which applies in some, but not all, cases... when a question as you've just asked relates to politics, in particular, U.S. politics... people (myself included) tend to get "pissey" about certain opinions when those opinions ultimatedly could lead to a loss of personal freedoms.
Case in point... I'm an avid shooter. Been shooting my whole life, including the seven years I spent defending freedom in service of our nation in the Army, it's a hobby for me. But with that said, as much as I'm a supporter of the second amendment, I am also a law abiding citizen... so when people see something like what happened in Tucson recently (less than an hour from my house) and try to use it as a means to further their personal political agenda that guns should be outlawed because of the actions of one nut-case... yeah... it tends to piss us off and make us argumentative.
One of the unfortunate side effects of "freedom" is that, while most of us sane and rational people see our freedoms as a means to improve our own personal lives, nut cases like Jared Loughner can also use those freedoms to commit horrible acts.
People who try to turn acts commited by freaks like him into some sort of political motivation to further their own OPINION oriented agenda of one form or another (i.e.- guns should be banned) into actual legislation that affects ALL of us are just A$$HOLES that should be dealt with and argued with accordingly.