First of all, it’s important to understand that the fight for legalized homosexual marriage and likewise the fight for allowing openly homosexual soldiers in the military are not radical in nature. Sure, these fights are liberal, but fundamentally, they are assimilationist, which is basically attempting to join the current system of privileges, rather than changing the system in any significant way.
Gay marriage advocates do not seek to restructure the social or legal benefits of marriage, they only seek to expand those benefits to all monogamous adult couples. However, even for those radical liberals who may oppose the institution of marriage, there is good reason to support gay marriage advocacy. The institution of marriage is so strongly enshrined and honored in world culture, that having homosexuals in recognized marriages will help to normalize homosexual relationships in a way that nothing else can. Married same-sex couples will significantly expand the cultural awareness and acceptance of those relationships and the legality of their relationships will help drive more important legal protections (e.g., if same-sex health benefits became legally required due to marriage, then other anti-discrimination laws such as for housing and employment will quickly become universal, as has more-or-less been the case in Massachusetts).
As for gays in the military, here is a short video debate between Mattilda (radical) and Dan Choi (gay soldier pragmatist) for some context: http://www.democracynow.org/2010/10/22/does_opposing_dont_ask_dont_tell
Gays in the military advocates do not seek to restructure the military methodology of extreme and diffuse violence at political behest, nor the mindset of uncritical machismo, they only seek to expand the benefits of a military career to openly homosexual membership. However, even for radical liberals who recognize the significant flaws of the current military complex, there is good reason to support gay military advocacy. Military service is so strongly enshrined and honored in U.S. “patriot” culture, that having openly homosexual service members will help significantly increase visibility and perception of homosexual individuals. Out gay soldiers will be recognized and celebrated for their service and sacrifices, and in response the most traditional and patriotic among us will give them some measure of respect. Likewise, if homosexuals can give their lives for the country, that can help drive other legal privileges for homosexuals (e.g., same-sex relationship sickness visitation rights). In addition, having more women and open homosexuals in the military will help erode the misogynist machismo that pervades the current military complex.
That’s why us radicals who may take issue with the institutions of marriage or military, should still support allowing homosexuals into those institutions. Not only will it help gain acceptance for homosexuality in general – thereby pushing culture in a more liberal direction and driving other, arguably more important, gay rights efforts, but to paraphrase Dan Choi, when you’re excluded from a club, your objection to the existence of the club is virtually meaningless – when you’re entitled to membership, then your objections can be heard.