It gives the boot to people who want to serve on their own terms. Until DADT changes, you are permitted to serve in the military, even if you are a homosexual, so long as you do not "come out of the closet."
As for holding personnel responsible to the commitment they've made - I think one of their commitments is "don't tell."
Is that really analogous? We had Buffalo Soldiers and similar units. I'm not aware of a Brokeback Soldiers regiment. This is an individual issue, not a class or ethnic one dealing with desegregation. Homosexuals can already serve in any MOS with all of the opportunities as heterosexuals. That was not the case with American Soldiers who were black prior to integration. DADT is based upon behavior (disclosing one's sexual preference), not characteristics bestowed at birth (skin color, gender).
Either way, I don't see how we can reasonably view this outside of the larger context that the debate is occurring in. This is part of a larger cultural and political fight. The military is being sucked into it. DADT is a battleground in someone else's war. Rather than getting involved in the debate, I think the military should be telling groups on both sides of it, "go find someplace else to fight. We're a little busy."
I suspect the difference is half due to different views of the military and half due to different views of homosexuality.
I have discussions about this stuff with a lot of people who are involved in LBGT legal issues. What I keep telling them is that they're trying push the law forward and drag the people with them. It is much easier to lead the people forward and let the law conform. Forcing social change through legal maneuvers generally doesn't work without some significant fighting to come to a consensus before hand. The Civil War amendments followed a civil war. Full recognition of minority voting rights followed significant social upheaval. The example that I keep pointing them to for a non-violent alternative is the environmental movement. It's been going on for 40 years. Now people embrace it without any coercion or incentive. There is something to be said for patience. But I guess when the law is your only tool, then everything looks like a legal issue.
It may be a generational thing as Marc points out. I don't think the torch has been passed to a generation that is ready for this.
Bookmarks