I actually served in the military.
Will The Repeal Of "Don't Ask, Don't Tell" Law Eventually Corrode Military Discipline And Readiness? No--Don't ask don't tell has only been around since the '90s. The military did fine before that.
Will the repeal adversely affect future recruiting goals? No; there are a suprisingly high number of homosexuals already serving in the military
Will fewer current servicemen and women re-enlist? No; this new generation is far more progressive than previous generations.
Will the all-volunteer concept go by the wayside and the draft have to be re-introduced? Let's hope so
Consequently, is the repeal dangerous for national security? No; but if you're concerned about national security, I can direct you to the nearest enlistment office