Its about setting a good example for the children. If children grow up watching porn where everyone is wearing condoms, then they will use condoms themselves.
Wait a minute... You let your children watch porn?
If they're old enough to legally watch porn, then they should have known better. By that time, they should have had a few sex ed classes in them from the good old education system, and you, as a parent.
Bottom line is, if your kids fail, it's because you're a gigantic failure yourself. Stop trying to blame others for your failures, and stop with the silly legislations that take away my rights to watch porns without condoms.