Your answer is how many Americans support the homosexual agenda? Very few.
A homosexual serving in the military isn't wrong. An OPENLY homosexual is. There has always been homosexuals in the military. However, they did not broadcast it because they honestly wanted to serve and NOT engage in social experimentation. What is going on now is all about forcing society to accept them as normal. They are not.
Which is why "I support the continuation of DADT. It has worked well for two decades" would have been the best and most straightforward thing for Santorum (or any other candidate) to say.