What happens when the U.S military throw out troops who are homosexual and either by their choice or a number of unfortunate events that caused them to be found out?   The government must provide the funding to discharge them.   Not many people understand the amount of work and money it takes to discharge somebody, this process can take months.   Not only does the government have to provide funding to discharge the service members, but they must also provide funding in order to recruit and train new people to replace them. 
     Someone else in the class is doing their research paper on Americas Debt, and I think that this ties into it.    The DADT isn't to blame for all of America's debt, of course, but it is sucking some of the money out from our nation's budget.   We could save millions over the years by the repeal of this policy.

The cause is the "Don't ask Don't tell" policy, and its effects are hurting our nation by using unnecessary government funding.
You could also look at it this way:

The cause of the repeal of the "Don't ask, Don't Tell" will effect our nations debt, and contribute to the solution to our nations debt problem. 

     There isn't a specific group or type of people that oppose the repeal of this policy.   There are high ranking officials that agree with it, then there are other high ranking officials that oppose it.   The same goes for experts, service members and the general public.   
     The claims that they use for the opposition are that it will harm unit effectiveness and cohesiveness.  Many believe that front-line men and women shouldn't have to worry about this, and the military isn't a place for a social experiment, especially in a time of war.
    A retired colonel believes that the military is much more conservative and attached to traditional values then general society and that the repeal would eventually lead to allowing same-sex couples to have benefits, such as allowing them to live in family housing on base, and it would disrupt the good dynamic it has. 
     Many go as far and dramatic as claiming that this repeal will ultimately disrupt and destroy our military.