In libertarian philosophy, choice is always preferred and coercion is always shunned. So whether it's a ban on plastic bags or recreational drugs the operative word "ban" is antithetical to libertarian thinking. Even a surcharge on plastic bags rankles most libertarians. There must be a better way to change behaviour if that is a goal.
I'll put aside for a moment whether plastic bags are desirable or not (here is an opinion I would support). Personally, I have no problem with plastic bags, but if I was a store keeper, I would at the very least offer a choice, like they used to: paper or plastic, very sensible.
Of course store keepers feel compelled to abide by the government edict that prohibits "free" bags and they feel no obligation to offer a choice. Why? Because they were not offered a choice, and orders are orders. But imagine the goodwill that customers would feel if indeed some entrepreneurial store keeper started offering recyclable paper bags to their customers in the spirit of "you can catch more flies using honey than vinegar."
Some people at Volkswagen had thoughts along those lines a while back, so they sponsored what they call "The Fun Theory." The video below was part of that enterprise which causes people to change their behaviour if they are incentivized to do it. Watch the video and go see the others here.