The government still needs people to enforce their laws, you can't use fighter jets, bioweapons, and nuclear weapons against your own citizenry without losing legitimacy and leading to a civil war where foreign governments would arm all sides. Take a look at Syria, they successfully overthrew the Assad regime with the support of other nations.
We currently have armed unidentified state thugs snatching random minorities off the streets, that's the sort of government abuse that could be stopped if liberals were armed. The state can only go so far in using force against their own citizens before it fractures and we look like the Syrian civil war.