Nothing in the guidance says that you have to "mask, social distance, and not gather indoors" - just to avoid actions that are _massively_ likely to spread a virus (from an asymptomatic carrier to either a potentially-symptomatic carrier - who a) will actually suffer from it, and b) will incubate and carry the virus for longer, thus spreading it to more people - or to a _bunch_ more asymptomatic carriers).

A lot of people don't seem to realize that "vaccinated" isn't the same thing as "not carrying the virus". The virus is going to die off _faster_ in a vaccinated body, but not immediately. It still makes sense to be cautious (but not _so_ cautious) with that lower (but still non-zero) risk of being a carrier/spreader.