Grenades are rare, but they are some who uses them. Of course they are not your average bum looking to rob $5 from a pizza delivery boy.
The big drug cartels that operate in Mexico and across states such as Texas does use grenades. They sometimes build the weapons in Mexico and sometimes they buy them from Central American countries that previously had civil wars.
Do you think such groups are going to see a "no hand grenade allowed" sign and just leave their boom eggs at home? No. They will use them in the US all the same to protect their shipments. And they do.
But just as long as the US citizen is disarmed, who cares what other groups have or do. No one cares about what these people do to Americans living near the Mexican boarder.
You need proof for that, just start telling people those facts. And when they start denying it you will know they don't give a damn about what is going on. If it's not on the big screen at their finger tips, they are clueless.