Soviet (right) and Nazi officers celebrating the joint invasion of Poland as their countries both embarked on a genocide of the Polish people, Brest, modern-day Belarus, 1939
Both the Marxists in the Soviet Union and the Nazis in Germany tore down their countries and rebuild them in accordance to their tyrannical ideologies. It's a stretch to call regimes that brought radical change conservative when they clearly not for preserving anything from the previous regimes.
In both cases, they co-opted popular left-leaning movements to engage conservative voting bases. They combined these popular movements with nationalist conservative ideologies to garner wide appeal amongst conservatives.
After winning, they then used their momentum to tear down institutional checks and balances to make sure they would hold power indefinitely, even if their support started to wane. Conservative support, in both cases, remained strong for many years, resulting in the deaths of millions of innocent non-conservatives.
Not quite, IMHO, seeking the imaginary ideal of yesteryear is what conservatism is, everything new is bad. The right wing of any political system is regressive and also looks back to this same imaginary ideal.
The right wing of any political system is regressive
Yes, I completely agree. That's what I'm saying. I don't see how you can fix that other than universally disallowing the right wing of politics any influence over decision making, in which case the left will likely fracture in between its most left wing elements and it's most centre-left elements and the process starts again.
So unless you want endless purging of whatever happens to be on the right wing of your political spectrum, I don't see what the cure to Conservatism or the right wing is.