I agree with President Obama; the U.S. Congress should repeal "don’t ask, don’t tell" and eliminate any federal prohibition on gay service.
The usual argument made for excluding gays from the military is that, because of anti-gay sentiment among some non-gay soldiers, the presence of gays might undermine cohesion and discipline. No evidence, however, supports this view; gays have served with minimal problems in numerous countries (e.g., Australia, Canada, Germany, Israel, Italy, United Kingdom, Switzerland). The same arguments made against gays in the military were offered decades ago in the United States to oppose racial integration of the armed forces, yet these forces are now entirely integrated with minorities disproportionally represented.
Whether policy should compel the armed forces to allow gays to serve openly – or just leave the issue to the individual armed forces – is a more subtle question. A decentralized approach might lead to slower change, but it might also produce a less polarizing transition.