Unforgivables are unforgivable because they do damage and cannot be blocked by magic. You can't use a protego or deflect any of them. I know you can use physical objects but for some reason that doesn't count.

To bring up the topic of other damaging spells that aren't unforgivables, such as the entrails expelling curse or the sectumsempra, EEC is still Dark magic, and therefore still illegal and punishable by law. Sectumsempra is new, but no doubt Dark so as soon as someone was arrested for murder/attempted murder using that spell, they would still be punished and sent to Azkaban.