Why are you in favor of "Don't ask don't tell"?

I'm a straight former marine combat vet and a student of history and not all gays are "sissy men". Alexander the Great had a whole regiment of gay males who fought to the death and were feared in battle. I knew 2 gays in the marines and what they did off duty did not reflect on their dedication to the Corps for they did not bring it on duty. I think the don't ask don't tell policy is better than none at all but admission should not be a reason for discharge.