Definitely a growing trend in the USA. If you are a "mask bouncer" at an establishment that has set requirements of wearing a mask to be able to enter and purchase goods - then be prepared to get shot at or at least broken bones.
Not going to post links, because I get the feeling there will be hundreds if not thousands of examples soon enough.
Personally: I get the feeling that many ex-gulf war types (seem to be the most likely to get deadly aggressive) know how often they have tainted the everyday supply chains of other nations. Do onto others as you would not want to have done on yourself? Probably that and a combination of many US citizens (white males specifically) not being used to the idea of being told "No" at the door.