That’s how you build natural immunity.

Not everything you’re infected with gives you benefits, there are a vast many transmissible infectious agents that can literally kill you. While the chances of licking your finger in a grocery store and getting something that bad are pretty slim, it does happen, and your “natural immunity” is working all the time anyway, you don’t need to DO anything to help it along, stop thinking you know better. If you’re annoyed with how other people handle their hygiene, how about be an adult and keep quiet.