Economics has this concept called revealed preferences[1]. These are preferences that people don't say that they want, but is what they actually use preferentially. An example of this the ordering machines that you normally now see in fast food places these days. People often say that they'd rather order by a cashier, but when given the choice of using one of these machines, or waiting a few minutes in line to get a cashier, they overwhelmingly choose for the automated option.

Tying this back to your first point, the revealed preference is that people would rather fill their own gas tank, rather than be forced to wait for someone to come and fill it for them.

Bagging groceries is different, however the revealed preference is that people would prefer the lower price/lower service supermarket, and those that need the help have to ask for it.

You are correct that everyone needs to earn a living, I think that most people would prefer that others can earn a living doing a somewhat meaningful job, in a somewhat safe manner.

The reason that much of this isn't automated has nothing to do with ensuring that jobs exist, but rather that the cost of automation is higher than the cost of labour. This is what op is talking about.

[1] https://en.wikipedia.org/wiki/Revealed_preference