Firstly, your comparison of Ayn Rand, a deceased novelist, to multi-decade tyrannical dynasties, is more than a little unhinged.
Secondly, the way that people act is strongly influenced by their surroundings, institutions, and social context. To think otherwise is the Fundamental Attribution Error. Castro and Kim don't have some special quality that would make them totalitarian dictators in the future; it's the nature of Cuban and Korean social institutions that have put them where they are. In a not-so-very-different world, Bashar Al-Assad would be an ophthalmologist in Acton. If future institutions are sufficiently inadequate, there will be plenty of would-be tyrants without worrying about a few cryopreserved relics being some sort of tipping point.
Thirdly, I suppose it depends on your view of mankind. There is no realistic way you can control whether people who are cryopreserved (or born) will be "good" or "bad" on net. So will, on average, more people lead to better outcomes? Or are human beings some kind of virus?
This month's media thread includes a short article on some people's idea to have Ayn Rand frozen, which ultimately didn't happen. My first reaction was a shudder. I thought, I definitely wouldn't want Ayn Rand preserved forever. My second thought was, What right do I have to say who can and who can't get frozen?
Whatever your thoughts on Ayn Rand, I think this can spark an interesting conversation: What, if anything, should humankind do about people who are widely seen as harmful for the whole? For example, if the Castro dynasty in Cuba or the Kim dynasty in North Korea decide to freeze themselves to ensure they will continue oppressing their countries forever, should that be prevented? (And yes, my opinion of Ayn Rand is such that these examples came to mind.)