Body temperature scanners are questionable at best because a very large portion of people with the virus will not show symptoms. We do have testing. I know it's not consistent, but every person I've known that wanted a test after being exposed to someone with the virus has been able to get a test. As of today, we have more ventilators available than there are people that need them. Anyone saying the medical system is overwhelmed is full of it. Hospitals are going under and nurses/doctors are getting laid off due to lack of incoming patients.
As far as testing a percentage of people, who's to say who gets tested and who doesn't? If not every person can get tested, which they can't, there will always be people carrying and spreading the virus without knowing. Now I'm not saying testing is useless, it's not at all useless. But it is also far from the solution unless we administer mass testing for everyone who steps out in public. If everyone was able to get a test every time they left the house, the virus would be defeated in no time. But the reality is that that's not even remotely a possibility.