According to WaPo, it's an ironic bill, apparently:

A Missouri lawmaker who’s introduced measures that would force adults to own handguns and young adults to own AR-15 semi-automatic rifles said he’s trying to make the point that mandates are bad and doesn’t actually want to require gun ownership.

“The other side of the aisle loves mandates, so I’m trying to get them to make an argument against mandates,” Republican state Rep. Andrew McDaniel, of the rural Bootheel community of Deering, said in a telephone interview.

It says a lot that this man considers "must have healthcare" and "must have gun" to be equally ridiculous.