Remember, every time something is banned, we're raising the price of whatever is affected. Lots of people have the luxury of having cost as a secondary consideration (myself included) but many don't.
And although many are going to want to say "But what price the future of our planet?" just imagine you're now saying that to someone genuinely struggling to feed their children and think twice before bringing your financial privilege into it.
And no, I don't think banning "single use" plastic bags is going to dramatically affect anyone individually, but I do believe that the ever growing feeling that we need to ban anything not "environmentally friendly" will at some stage have real social impacts...
Although it doesn't fit into the environmental camp, for a real world example of this let's just wait and see how many families will no longer be able to justify fresh eggs when all supermarkets only stock free range at 2 or 3 times the price of caged.
Cheers - N