At the risk at becoming boring on this, the medical reason goes like this: either pubs can be open (until 10), or your wife can visit her mum (and by extension everyone is allowed to visit other people etc). The allowing of either category of activity will result in a number of infections which is acceptable (in terms of controlling exponential spread), but twice that number (ie if both activities are allowed) is too many.
The calculation is then which activity will be more beneficial to society overall - here there is a value judgement that pubs being open (combination of social interaction, good for mental health, and economic activity, good for livelihoods and still having a functioning pub sector to come back to when all this is over) is overall more beneficial than alllowing people to meet in their homes (social interaction only, primarily) (I am aware I am simplifying at almost every point here but the principle is I believe sound).
This calculation is done on a societial basis,so in the short term at least there will always be some people disbenefitted (those who don’t go to pubs for instance). However assuming the inputs and assumptions are correct, it should be the best overall result. One can always argue the inputs and assumptions of course and here it becomes politics. But there (or the first half of it anyway) is the medical reason.
Short version: Scientists say we can do X or Y (but not both), politicians decide which we get to do.
I was somewhat sceptical about mask wearing before. I would still prefer not to. It's a bit uncomfortable especially wen wearing shades and travelling for a few hours but as it appears it does have some benefit, gotta be done.
