I do not think that mandating gun ownership is a good idea. I think the RKBA also carries a right to not keep or bear arms, just as the right to free speech includes a right to not speak.
Tax credit . . . gee, however will the IRS decide whether someone is qualified? Oh, yeah, by requiring a list of firearms, complete with make, model and serial number.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.