But yes, I agree with you that saying "it's good because it's old, bad because it's new" is illogical.
I don't think many people are saying that though. If people are convinced that a new thing is good, the change happens. I think people are much more likely to suggest that change is good simply because it is new, which is also dangerously illogical.
People were convinced that the new USSR was good, so it happened. Dictators will undoubtedly happen again, and they don't get there by keeping things the same.
I think it's very much the reason why God/tradition "appoints the king/queen". - The age old tradition is larger than any individual's life, and theoretically keeps the "dictator" in line (as long as we all respect that tradition).
If there is a new period of change with a new leader then anything is possible, subject to human motivations.
The illogical reasons are the ones which reduce to "It's bad because it's new" and "It's good because it's old" with no further content, just rhetorical smoke bombs and hand-waving.