Well, they would most likely use a measured response. A common sense force continuum. Up to and including lethal force if justified.
Most times. The ability and willingness to use force, is the best deterrent.
If justified force becomes necessary, it's good to have all options on the table.
At the end of the day, the citizen militia is subject to the same laws as anybody else. If lethal force is used, it will be investigated like any other situation.
It's the common sense alternative to seeing the police overwhelmed, or hobbled by ROE, while the anarchists wreak havoc on your town.