This seems like an important balancing factor in Rook City. The built-in destruct clause of Twisting Back Alleys is basically suicide, and Scum and Villainy is another one you don't want to get back around. Toxic Sludge is heinous all by itself, but at least it holds the heinousness of the other cards in check somewhat. It even gives you a discount on destroying Blighted Streets as well as bypassing the need to skip dealing damage for a turn, although it can't do anything about the free villain card.
(I need to try sending Warlord Voss to Rook City sometime; he might end up deciding Earth isn't worth the bother of conquering.)