The title of this post - as everyone knows- is "Why get personal when discussing a topic?" Not for the sake of argument, but for the sake of opinion, this question is correct but is somehow missing one point: sometimes you have to get personal if the topic is very dear or affects you personally.
Just to use a very common example, try asking a survivor from a concentration camp not to get personal about the Nazi. It would be very difficult. Even if the person were to constrain personal thoughts to cold analysis, the person would still be personally involved.
Also, some topics outrage people.
Even so, it is absolutely true that we all should at least strive not to resort to name-calling and discuss the matter at hand, not the person.
I am often very much in disagreement with things that are said here regarding politics towards Latin America. I feel that quite often people do not really understand the issue or see it from a simplistic perspective. So I need to be very much aware of what I do myself to avoid the name-calling and the ad-hominem and et cetera.
Incidentally, because of recent political developments in the region where I live, I realize that we Latin Americans are also simplistic in our opinions about events elsewhere in Latin America - or the English-speaking world, for that matter, which, I am afraid, not many of us really understand either.