Two problems: first, if you're just going to query ARIN before sending nastygrams, then RIPE will hate you, because ARIN think that huge chunks of address space belong to RIPE when they don't. I assume that they think the same about APNIC and LACNIC too.

Second, automated nastygrams are Just Wrong. You can, of course, automate whatever you want within your network, including blocking great big chunks of addresses, but if you send out nastygrams without *detailed* human checking, then prepare yourself to be blocked in turn as an abusive network.