It's all about the modern day mentality of the "bad guy as a victim," and the knowledge that a prosecuting attorney will do any and everything within their power to make you look like the big, bad, bloodthirsty gun owner, who was just waiting for an opportunity to shoot someone - anyone.
If you use reloads, it gives a prosecuting attorney room to say you worked up a special "hot" load, even if you were to shoot the BG with a FMJ round nose round, and loaded at the lower end of the performance spectrum for the given caliber of weapon you were using. At least, using mass produced ammunition gives your attorney the wiggle room to say something like "My client selected this round because it is used by many Law Enforcement agencies," or something like that.
To nutshell it: Using mass produced ammo gives the prosecuting attorney less room to accuse you of bloodthirstiness,and you more room to proclaim your innocence.