That depends on where you stand at the beginning.
The history of Canadian gun control, proves the slippery slope exists.
Well, in Canada what has been shown is that registers are used to confiscate guns which they ban. What has not been seen is that this leads to banning all weapons, or that it necessarily leads to confiscation. After all, the long gun registry was scrapped, so doesn't that teach us that registration leads to de-registration?
Let us not make the post hoc fallacy relating registration with confiscation. That is what Colpy was doing, and I am willing to drop it to discuss that confiscating guns is sometimes a necessary evil.
Consider that anything that we eventually decide must be illegal to possess will go through a phase where possession is legal. If someone happened to possess the thing before the decision to make it illegal, then it needs to be confiscated somehow or grandfathered.
Drugs, bombs, cannons, guns, knives, crossbows, vehicles, art. There are examples of all of these things that were once legal but subsequently made illegal--in all the countries I know even the littlest bit about.
Of course, I am against total prohibition of anything. Specifically on topic, I am for gun control, not gun prohibition.