Because you will;
1. No longer be spammed with dozens of 'friend requests' to buy BiS(now BOA) gear from botters.
2. ALL channel won't be swamped with trade spam from botters.
3. Scammers will also have the above same problems.
4. BOA means much less reason to hack you account for gear.
5. Too many other to list.
Doesn't take a genius to figure out what hurts botters/scammers is in general GOOD for everyone else...
I don't know about this... In WoW, they basically completely devalued gold (other than for aesthetic items and such), but this did not stop gold spam.