It isn't such a bad idea, especially for the hearing enhancement. I think, however, that we're overestimating the effect of gunfire, particularly what you're likely to use in a HD scenario. If you look at any of these news reports about SD/HD shootings, you come up with one, two, or *maybe* three shots fired. Shooting a burglar/rapist/murderer is not too likely to be a battle for Iwo Jima type situation. You'll expend a few rounds, your ears will ring for awhile, and then you'll be okay.
While serious hearing damage can come from a single loud event, you are more likely to damage your hearing by chronic exposure to noise just above the damage threshold. I believe that's 85dB. Lots of work around loud engines (I'm talking about bulldozers or race cars, not jets which are well above the threshold), loud music, power tools, etc. are a MUCH bigger threat to your hearing than a couple of gunshots because you're not likely to think it's loud enough for damage. Thus, you will not use any kind of hearing protection. I'll cite my grandfather as an example. He landed at Normandy, but he has always protected his ears when working around loud machinery like the trucks he drove for four decades. He's now 82, watches the TV with the volume way down, and can hear me talking quietly across the house.