It's a logical mistake to say that because an extremely motivated person can still cause harm somehow that implies no regulation or policy can have any positive impact anywhere.
I don't have a stance here on what "the right" policies around gun control are but it is clearly a much wider field than just a preplanned assassination with diy parts.
A non-exhaustive list of a few very different scenarios that are all involved with anything touching or rejecting gun control:
- highly motivated, DIY-in-the-basement assassination plots like you mentioned
- hunting for food
- hunting for fun
- wilderness safety
- organized crime and gang related violence
- mass shootings at things like concerts, sporting events, colleges. Sub point of mass shootings at schools where the law requires children to be.
- gun violence involved with suddenly escalating impromptu violence like road rage and street/bar fights
- systematic intimidation / domestic terrorism of particular groups or areas
- gun related suicides
All of these are very very different. None of them have perfect answers but that doesn't make thinking about it "an act of banging your own head against the cold, hard wall of reality" nor does it make anyone interested in working on some of these problems naive or stupid like you imply.
If you're being earnest or maybe jaded, I'd say dont give up hope and don't let perfect be the enemy of good.
If you're just being a dick then so be it, maybe someone else gets something out of this comment.