It is about the belief that you "don't give Mr Rogers any power you wouldn't give to Hitler." Basically no matter how great you think your current leader is, you recognize that they will not be in power forever (or that they may not be good forever). Democracy, autocracy, oligarchy, whatever your system of government, there is a singular truth: all men die. All things change. Obviously this policy can go too far, but personally I think it is worth considering not just how good a policy or power can be, but how much harm it can do if abused or misused. It is easy to ignore this part because we want to believe people are good and have good intentions. Because we see the advantages and get excited about them. Because it is harder to think about abstract scenarios. But it is an important thing to think. You need not think your government is evil or nefarious to still be concerned with turnkey tyranny. In fact, the more faith you have in your government, the more you should be concerned. Because it is at that time that people are less likely to keep their guards up, and it is that same time that hostile actors look to take over. There is no absolute defense against malicious leaders, so it takes constant care.