Because Deca is so damn suppressive! Theory?!?! Come on. Everyone knows this. Plus, Deca kills sperm cells at a rate that's like 10 times higher than test. (Don't have the studies in from of me, you'll have to search). It bloats. It raises prog. It causes impotence. I'd say that makes it harsher on the reproductive system than drugs without those side effects, wouldn't you say?