I felt bad for enjoying it. Worked from home, hardly expected to go out, much less traffic. Most service related jobs I prefer to do myself (like haircuts like you mentioned) or am perfectly fine with minimal contact. In general I feel bad for service workers so even if they aren't friendly with me (not that I ever really experienced that much) I wouldn't mind, and also don't mind self checkout and automation.
I may sound like I'm accusing others, and maybe that's part of it, but the way service workers are expected to act certain ways with us feels like trying to perpetuate class based servitude. As long as they're relatively professional and not outright insulting, I think it's fine.
I always try my hardest to look a service worker in the eye at least once during our transaction. Just an unconscious way to let them know I see them as an equal, not as a servant. I realize that's not making a major change in the world, but I figure they don't get that much.
That definitely helps from anecdotal information I was told, and I do the same. One of my younger sisters worked at a sorta prominent restaurant in Atlanta, and she complained that some of the high end clientele refused to look her in the eye. Sometimes she found it so insulting she'd act like she didn't realize they were talking to her until they made eye contact.