Don't ask don't tell (DADT) does not prohibit gays from joining the military.  There are gays in the military right now, showering next to those that are not gay.  Until DADT's inception, gays were summarily disallowed from serving.  DADT changed that, though it stopped far short of actively recruiting gays and allowing those gays already in the military to openly declare their sexuality to their superior officers and the mess hall.  

Having said that, I think that the military should be a place that evolves on its own.  I see no benefit in using our armed services as a venue in which to force progressive policies not specifically aimed at bettering the military itself.  The military operates, for good reason, generally outside of society. It has its own rules and regulations. It is not a laboratory built for the experimentation of politicians.  

Having said that, when the military gets to a point in time that gays would not be an issue to most people in the military, the change probably could be made with no harm done.  But that assessment can only be made accurately by those military.