Folks that are not supporters of the RKBA often come to that conclusion because they do not trust themselves or others to have weapons that can be so callously dangerous, and who in many cases inherently do not understand firearms. Some come at this viewpoint for personal reasons, and many others because of groupthink.
This groupthink is not unique to the foes of the RKBA; it's a characteristic of the human race and it's not restricted to the RKBA issue.
The net result of the erosion of empathy for firearms is that masses of folk are being conditioned to accept a 'protective' caste of police and military as a normal and desireable condition. So long as they accept that state of affairs, they will never grok why the RKBA has any value.
This is a viewpoint held by both the self-described conservatives almost as much as liberals. It *is* statistically more prevelant among those who claim to be modern liberals, but it's not a 'liberal' condition. It's a 'statist' condition, and statists exist in both parties and across the political spectrum.
Because "liberals" like to live their lives in fear
No. They want to live WITHOUT fear. As long as they
believe that they are protected by the police and military and other .gov entities, then they can live without fear. And, frankly, the law of averages pretty much means that many of them
can live out their lives without ever being assaulted or worse - thus validating their perspective.
They fear YOU - the guy with a gun. They don't need one, because the cops protect them. Why should you need one? Doubtless, they conclude, because you intend to predate upon them. And so they seek to de-fang you, in the mistaken belief that it places you on equal footing with them.
Only when they are forced to confront the failure of their premise - that they are NOT actually safe in their little bubble - will they grok that they have only been the sheep in the center of the herd and that the fact that they didn't see the wolf wasn't because the wolf wasn't there but because their vantage point was occluded.
Of course, you will always have those statists who wish to disarm the common folk to make social reengineering more successful. They will never support the RKBA, and they exist in all political folks pretty much equally (seeing as how they are usually political opportunists who have fewer core values and simply maneuver for power).