[Lurking Libertarian]

On the other hand, since federal gun laws are not an issue in this case, it's actually up to voters to spur their state lawmakers to make gun laws which reasonably limit gun rights with respect to the example of this case. Letting the Supreme Court decide this case just gives activist justices an opportunity to unconstitutonally expand federal government powers imo.

It is a federal law which is at issue in this case, which is why it's before SCOTUS. The statute is 18 U.S.C. § 922(g)(9), which makes it a federal crime to possess a gun if you were previously convicted (in state or federal court) of a “misdemeanor crime of domestic violence.” Different states define "domestic violence" differently, so the issue before SCOTUS is what state crimes qualify-- only those involving serious physical harm, or those involving less serious kinds of force.

The Court is not considering a constitutional question in this case, but only an issue of interpreting what Congress meant (which means that Congress could clarify the statute if it doesn't agree with what the Court decides).

[Amendment10]

It is a federal law which is at issue in this case, ....

Mea culpa. Thank you for the clarification and the additional information.

Please indicate which constitutional clause expressly delegates to Congress the specific power to regulate firearms for ordinary citizens. There are no such clauses imo.

Again, the 14th Amendment only gives Congress the power to strengthen constitutionally enumerated privileges and immunities, including the 2nd Amendment.