A phobia is an irrational fear. It is occasionally argued that the source of negative views of homosexuality is the fear that one might have homosexual inclinations, but it is a considerable stretch to claim that source for all negative views. It seems obvious that some people are opposed to homsexuality because they think their religion condemns it, some because they think it has bad consequences, and some for any of a variety of other reasons. Labelling all of them "homophobic" is a way of (falsely) implying a single cause for the conclusion--and, by doing so, attempting to stigmatize all those who hold it and dismiss all possible reasons they might have.
A second example is the term "racism." In a recent exchange here, Mike Huben referred to "racist science" in a context where it meant "(hypothetically) correct scientific research that demonstrated the existence of differences among the races" (if this is not a fair summary, I expect Mike to correct it). That was a striking definition of the way "racist" is used to mean, not "hating or despising other people because of their race" but "holding beliefs on racial subjects other than those of the person using the word." Again, that usage is an implicit argument and a dishonest one, since the implication again is that the only possible reasons for disagreeing with the speaker's views on the subject are bad ones.
The pattern is not limited to people whose politics I disagree with. Libertarians do the same thing. In our context, the question is how to label people who disagree with libertarian views, on particular subjects or more generally. The two popular choices are "statist" and "collectivist."
Both are wrong. There are lots of reasons why someone might favor the draft, or minimum wage laws, or price controls, or the war on drugs. Worship of the state is no doubt one possible reason, but certainly not the only one. Belief that what really matters is the collective and not the individual is one possible reason but not the only one. Each of those views could readily be held by someone who agreed on the whole with libertarians about values, outcomes they wanted, but disagreed about the consequences of particular policies. Most obviously, someone might favor the draft because he believed it was necessary in order to defend the U.S., and want to defend the U.S. precisely because he was in favor of freedom and thought the U.S. was much freer now than it would be if someone else conquered it.
In each of these cases, the pattern is the same. We have a conclusion that might be reached for any of a variety of reasons. Someone who wants to attack the conclusion does it by picking one reason he considers particularly unattractive and indefensible, using that reason to label the conclusion, and thus (dishonestly) implying that anyone holding the conclusion does it for that reason.