A duck!
who are you, so wise in the ways of science?
It makes assumptions which don't seem reasonable in the context of the subject matter at hand. If aliens did exist, they could be much more numerous than humans. Their spacecraft could be more dangerous than airplanes to operate. Their method of travel could perhaps result in collisions with Earth even if it wasn't their intended destination.
My overall point is that we should minimize the assumptions we make here. There's no point in assuming various things and then proposing arguments based on those predicates.
We can't assume that getting "help" is trivial just due to the volume of travel. Commercial airplanes can't rescue each other, just as an example.
I don't believe that aliens are making contact with Earth. But I don't find your argument against that possibility convincing either.
In my mind, a much better argument would simply be that with 7 billion people on this planet, the likelihood of alien crashes staying secret seems miniscule. We would have solid conclusive evidence already if it had happened multiple times, like alledged.