Read the category of Necessary Evil. It says, and I quote; "Amoral entities that must keep the balance of nature in check (Almost every incarnation of the Grim Reaper or any Death God in mythology is this)." End Quote.
And since Death is an Amoral Death God, he qualifies as a Necessary Evil.
But the problem with taht is that he doesn't do anything that's necessary. He doesn't keep the balance of nature in check. All he did was collect the Titans' souls which is actually unnesscary seeing as they were perfectly fine as ghosts in "Ghostboy".