"I'd prefer to argue FOR equal rights on the basis of the that being the morally right position"

This sounds like something that is true, but I'm not sure it actually is. The basic problem is that saying something is morally right is a statement, not an argument. If you read Jon Stewart Mill's essay On Liberty, he doesn't just say that free speech is morally right, but rather he proves it using practical examples.

For example, here is a good quote I found the other day about the political cost of bigotry:

"As important as the issue of bigotry is that this incessant vilification of gun owners precludes reasonable compromise over gun laws. The gun lobby press faithfully reports the philippics, and reprints the most vituperative anti-gun cartoons, to inflame its readers. Why would the gun lobby actually pay royalties to Herblock, Oliphant etc. for their anti-gun cartoons? Because the gun lobby's purposes are best served by convincing gun owners they are a hated minority. There can be no greater incentive for monetary contributions to the gun lobby and fanatic hatred of gun law proposals, no matter how apparently reasonable.

Gun owners are convinced (in part, by bitter experience) that gun laws will be invidiously administered and unfairly enforced; and, just as important, that gun owners are anathema to persons and groups like the ACLU to whom other American can look for help against mistreatment at the hands of the state. So gun owners hysterically oppose controls substantially similar to ones they readily accept for cars and prescription medicines. This is only natural, given the rancor with which controls are advocated and the purposes avowed by their more extreme advocates. Would driver licensing and automobile registration have been adopted if they had been advocated on the basis that having a car is evidence of moral, intellectual or sexual incapacity -- or that the desired end is to progressively increase regulation until cars are unavailable to all but the military and the police? Would not diabetics and others with chronic illness hysterically oppose the prescription system if doctors were under constant pressure from church groups and editorialists denouncing medication as immoral? Do not gay rights activists vehemently oppose policies (however apparently reasonable), they see as motivated by enmity to gays and likely to be administered in that spirit of enmity?

Two clarifications are in order here: 1) I recognize that cars, guns and medicines are different commodities that may require very different policy responses. My point is only that no policy, however rational in the abstract, can succeed if those it regulates see it as motivated by hatred, contempt and denial that they have any legitimate interests to be considered. 2) I also recognize that gun owners respond to anti-gun attacks no less hatefully. But there is a crucial difference: gun owners are not seeking to make their enemies own guns. In contrast, what control advocates do by heaping contempt on gun owners is forever alienate those whose compliance is indispensable if gun laws are to work. However satisfying it may be to anti-gun crusaders to portray gun owners as 'demented and blood-thirsty psychopaths whose concept of fun is to rain death upon innocent creatures both human and otherwise', the result is catastrophically counter-productive to the cause of gun control." -Don Kates

source: http://catb.org/~esr/guns/gun-control.html