Not to mention that at this point the science is so clear that it helps slow the spread, that wearing a mask should be common courtesy, good manners, and a show that your respect the lives of others.
And all that even ignores the fact that although it won't prevent you from getting it, it does at a minimum cut down on your viral load which may allow your body to fight off the infection or for any infection that you do get to be less severe.
So, it's a matter of both showing respect for others and yourself.
And as far as touching the mask, how hard is it to just wash or use hand sanitizer before you adjust your mask?