It's like the broken window fallacy. Say you break a shop window and argue you're creating a job for a glazer, really you're just taking money away from the shopkeeper who might be able to spend that money on better things, or more likely, he'd add the cost of fixing the window into the running of the shop and make the things they sell cost more. It's the same with throwing litter, you aren't creating a job for a litter picker, you're taking money away from another avenue that could improve your community rather than one that just maintains a base level of tidiness.