Well, in this case, a convicted felon is not legally allowed to have a hobby that entails "Collecting Guns".
Sorry, but I think you have had too much Kool-Aid to drink. If he’s a dangerous person - citizen or otherwise - he needs to be locked up. Conversely, if he’s free he must be no danger to the public and should therefor be free to collect all the guns, ammunition and magazines he wants - just like you should.