The benefit of masks is primarily that it reduces droplet transmission from carriers, many of whom are asymptomatic.

You can't propagate a droplet to your face by touching a surface and then your mask, if it never lands on that surface to begin with.

I'd really like to do away with this misconception: masks are primarily to prevent transmission, and only secondarily (and it's a distant second) to prevent infection.

Where did I say the primary purpose was to prevent infecting yourself? It doesn't help if they reduce transmission, if they increase the risk of infection at a greater rate. "It never lands on that surface to begin with." is a flawed assumption. You see people taking off/adjusting masks all the time because someone on the phone doesn't understand them, they want to eat something, etc ... or they retie the scarf they use as a mask and don't care which side is the "outside" ... and then go on to touch stuff in the store, and then again their masks ...

Like I said, I used to think it was a good idea, and now I've seen lots of people using the masks.