More than 1.2 American's currently have HIV. That's the documented cases, there are likely many more than are unaware of their infection
You could have said the same thing at the early onset of the HIV epidemic, people weren't "dropping like flies" in America after the initial outbreak in Africa. It's about preventative measures, not waiting until it's an epidemic like HIV/AIDS to take measures.
we've missed the boat on HIV, dude. no border policy will make a shred of difference in that regard. luckily for those 1.2 people, HIV isn't the death sentence it once was. it's is currently very manageable. i am friends with a few positive people, tbh. they lead normal and healthy lives.
as for ebola, if it was a real issue, it would become very apparent very quickly. this is unlike HIV in the 80's.