Unfortunately you're trying to argue with basic physics, which doesn't work.

If you're breathing out a virus, then my mask will lower my risk. But if you were also masked, it lowers the risk much further. (https://www.phc.ox.ac.uk/news/comprehensive-review-confirms-masks-reduce-covid-19-transmission)

Also your analogy doesn't work - if you're sitting in the back of a car and wearing a seat belt, you do reduce the risk to anyone in the front seats of a car.

A more suitable one would be allowing smoking back in buildings - I'm assuming it would also be your personal responsibility to protect yourself from my Marlboro?

Your last comment is particularly revealing - I'm guessing you're under the assumption that you'll be young, fit and healthy forever, and won't ever need to rely on society.

Unfortunately Covid is linked to an increased risk of new-onset auto-immune diseeases (https://www.nature.com/articles/s41584-023-00964-y), along with other viruses.

And not forgetting that it often includes those who are being treated for cancer, which is estimated at nearly 1 in 2 in the UK.

The immuno-compromised/suppressed have always had to take more precautions, and became sicker regularly. It just wasn't often talked about.

And the reason I still mask is partly due for my personal safety, and also because I don't want to infect anyone who might be more susceptible around me, particularly if I'm in a healthcare facility, for example.