Liberal ideals and authoritarian conservatism pull in opposite directions, putting the brakes on the AC impulse. Kind of like the way, in a star, the inward pull of gravitational collapse is counterbalanced by the pressure from fusion energy and products.

Conservative beliefs and authoritarian conservatism are aligned in the same direction, so there's no natural friction. Once it gets started the process is inclined toward chain reactions and runaway expansion.

The historical examples support the point: As you note, the Soviet Union imploded and all we had to do was be patient; while Nazi Germany exploded on to the world and had to be put back in the box through massive force.

Leaving aside the physics metaphors, there's a practical difference between the threat from either form of extremism: It's far easier to give up democracy and embrace authoritarianism than it is to move from authoritarianism to democracy (or to return from a sidetrip into authoritarianism). You only need one vote to give up democracy, while restoring it usually requires a revolution.

People generally understand, without needing fancy-schmancy terms like "authoritarian conservatism", that once you let a tyrant in the door, it's damn hard to get rid of him again, and that if the United States swings too far in that direction, we may never recover. An authoritarian conservative system is far too stable for its own good; that way lies stagnation.

The instability of Liberalism, while scary to the conservative mind, is actually the optimum mindset in a democracy, because its fluidity not only permits progress, it permits pulling back from failed experiments and trying something else. In an authoritarian regime The Glorious Father/Leader is never wrong, and so mistakes are rationalized and institutionalized as "the natural order of things".