I'm trying to replace a light switch in our kitchen. The lights are on a dimmer switch. Only one switch. The switch/box is bad, as it no longer works reliably (but will sometimes work if the switch itself is wiggled). So I removed the switch (after shutting off the circuit breaker

) and am in the process of replacing it with like equivalent (same manufacturer & model #).
But I noticed that the previous switch has had the green ground wire clipped. (See photo below.) Only the two black wires protruding from the back were pigtailed to existing wiring in the wall. Is that OK? Can I just wire in the new switch like the previous one and cap off the green ground? Or is this a fire waiting to happen?
Replacing the old switch with a new one and reinstalling everything like it was (2 black wires, no connected ground) works the lights, but the switch (or, rather, the metal tabs used to screw it into place) gets warm after a few minutes.