Questioning somebodies common sense when we disagree with them is neither nice nor nasty,
It's just common sense. Though the very term "common sense" is misleading, since in practice what is being referred to is individual judgements as to what we believe to be true.

The fact that a lateral test shows up negative isn't by any means a 100 per cent guarantee that we are infected and infectious, just an indication that we very likely aren't. And in any case that negative test doesn't show as to someone gets into a crowded tube train.

Failing to wear to wear in such circumstances seems to me a breach of common courtesy.

There are indeed times when we can feel obliged to do things that inconvenience other people or annoy them. Steve gives a set of examples, and most of them are things I've done, and would do again. You do them in the belief that they are in fact in the benefit of the very people you are inconveniencing or snnoying. Failing to wear a mask and social distance do not bein there