1. When mispallelim come to shul to daven, the expectation is that kaddishes will be said, hence the brief awkward silences that occur before people realize nobody is saying kaddish and they move on. Since people have already mentally given this time to kaddish, it cannot be a waste, and you are actually preventing awkwardness by saying it.
PLEASE! people must learn how to handle awkward experiences
but, great point you bring up!