So did I back in the 80's.
I've made numerous buddy breathing ascents from 20m. On my Nitrox course my buddy and I where buddy breathing on our 6m stop for practice (and to save some gas for my buddy with his smaller cylinder), whilst we waited for the rest of the class to sort themselves out.
I would not like to rely on buddy breathing in a real emergency, even with a practiced buddy I regularly dived with, it is very stressful and high task loading. Even during practice and exercise it was notorious for going wrong.
I carry a AAS for my buddy. I expect my buddy to have the same consideration for my safety as i have for his/hers.
This is even though I would normally dive either a twinset, or a CCR, which means i always have a redundant air source.
You are perfectly at liberty to dive without an AAS, just not with me.
I used to dive with a guy who only dived in wetsuits with an ABLJ, despite suggestions he should swap to a drysuit and BCD, not sensible in December in the UK, but his prerogative. I don't have an issue with how people dive, or what equipment they use, or how it is configured. As long as it doesn't put me at risk and they are considerate to the environment, start smashing the coral or the wrecks then I will have something to say about it.