The "not as bad as" argument, also known as the fallacy of relative privation, is a form of the moral equivalencefallacy that takes note of the existence of things that are worse than what is actually under discussion — for different purposes, as outlined below.
It's popular with people who know perfectly well they're doing something wrong; being fully aware that they're doing something wrong, they feel compelled to attempt to justify it and do so by pointing to other (usually worse) actions.
