I lock my doors when I leave the house. That won't stop someone who is serious about wanting to rob me. Anyone who has the necessary skill and determination can stake out my house, figure out when it's empty, then either pick a lock or use a hardware store glass cutter to get in and take what they want. It's not that difficult. I take security measures to make it harder for the casual thief to bust in, grab a few items and run. If the doors are locked and the windows are closed, that should be enough to discourage someone who isn't absolutely bound and determined to get in.
Making it harder for bad actors and people with mental illnesses to get guns won't keep guns out of all their hands, but it will stop a shooting here and a shooting there, which means a few people who otherwise would be injured or killed by gunfire will be spared. It's not going to reduce the 30,000 annual deaths from firearms significantly. But it's a start. And it will help keep the conversation going, maybe bend it enough that people realize the right for decent people to bear arms won't be impeded by measures designed to keep firearms out of the hands of people who plan to harm others.