I provided a reasonable alternate motivation.
No you didn't. Your supposed alternative motivation was fact-free nonsense.
There could be many, many other reasons
The fact that no one can provide any of these other motivations is evidence that no alternative motivations exist.
but safety concerns seem the most likely.
No they don't. Having a pistol grip on a rifle is not a safety concern in any way whatsoever.
On the other hand, doing it "for fun" seems very unlikely and I've never heard this from any source other than you.
The fact that no one can provide any alternative motivation is evidence that the only actual motivation is the fact that progressives enjoy violating people's civil liberties.
Since gun control manifestly does not devote "all its energy" to this effort
That is incorrect. The gun control movement routinely fights to the death on their need to violate people's civil liberties for fun. And in doing so, they often undermine all other gun control efforts.
One obvious example was the 2013 gun control debacle, where Mr. Obama wasted the entire first hundred days of his second term fighting over pistol grips, and by the time he had lost that fight, he had also lost on all his other gun control proposals as well.
Time after time after time, whenever the gun control movement is challenged on pistol grips, they stop thinking about other gun control measures and devote all their energy to their desperate need to violate people's civil liberties for no reason.
It's actually quite a convenient way of defeating gun control. Quite often gun control advocates simply defeat themselves with no need for heavy lifting from the gun rights movement.
What's really funny is, I can actually point this out to gun control people (as I am doing right now in fact), and even when they understand that I am correct, like good little lemmings they will still just keep on marching over the cliff.
In other situations I might have actually felt bad about their plight, but considering that gun control advocates are such horrible people (they actually enjoy violating people's civil liberties for no reason) it is actually pretty neat that they have an irresistible compulsion to undermine themselves this way.
your response is merely another instance of your penchant for posting self-aggrandizing drivel.
Pointing out leftist bad behavior is neither self-aggrandizing nor drivel.
Bye. I'll be here ready to provide facts again when you decide to return.