To some extent, it's because every time you take away gun rights, you're reducing the gun righter's group. Mostly, I think that it's a matter of slippery slope. Make no mistake, the anti-gun lobby is just as extreme as the pro-gun one, and they'd almost certainly keep trying to chip away at gun rights.
With labor, there's always that group there. When conditions get bad enough for the laborer, the exact same thing that made Unions powerful once will happen again. With gun ownership, it'd be a much more ticklish subject.
I've explained that crappily, let me go dig up an essay written by someone who is better at explaining it than me.
There is a wealth of accurate information that shows that gun ownership decreases crime.
There is a wealth of accurate information that shows that gun ownership increases crime.
There are several studies showing that most pro-gun studies are bullshit.
There is undeniable evidence that anti-gun lobbies astro-turf to an unreasonable extent.
It's certainly true that the NRA eats babies.
The Bradley campaign are a bunch of pinko-commies.
The 2nd Amendment is an individual right, just like the rights in the other first 10 amendments.
The NRA promotes lower back injures by wishing everyone carried a M2 HMG with them at all times.
There isn't a good chance that America will be invaded anytime soon, nor that an armed uprising of the people would be needed.
Your mom needs an armed uprising.