If you ban guns some people will get guns and use them.
That is a fact.
But much fewer people will use them then use them now.
And over time very few people will have access to them.
Especially young dumb high school kids with no underworld connections.
That is the point.
That is the most sensible approach. There's not going to be an overnight thing where suddenly 300,000,000 guns disappear from America. It's going to take a generation, and probably more to fix the problem.
This is also a cultural issue. American culture, among other things, is fucking violent. It's glorified and so often held up as the most efficient solution to problems. This runs the gamut from fists to warfare.
But we're not even close to solving the problem. Even if the semi-auto rifle were to be banned, it makes up a small fraction of overall gun deaths. They're certainly good for the most spectacular killings, but handguns by far account for most homicides e.g., a quick state from Wiki:
In 2012, there were 8,855 total firearm-related homicides in the US, with 6,371 of those attributed to handguns
This doesn't mean that people wouldn't begin using other types of guns to kill people, but handguns are far more concealable than any other type of weapon, more transportable, and can be had for pretty cheap.
Semi-autos are a first and probably "easiest" step, but getting rid of handguns would represent the real sea-change.
I own an even dozen guns, 4 of which are handguns. And I own an AK. I personally would give them up, but I account for tiny percentage of gun owners that would. I'm what's called a "Fudd." The moniker refers to Elmer Fudd, which has caught on as an insult to gun owners who support the idea of limiting civilian gun ownership to bolt actions, lever actions, and shotguns.
I bring that up because I have some insight into the mindset of even those who consider themselves liberals/progressives who are also gun owners. The vast majority of them march in lockstep (although with much less psychotic rhetoric---but often not) with your stereotypical NRA fanatic.
IOW, guns aren't going anywhere soon, so significantly diminishing the problem is going to take a long time.