Why do anti-vaccine people get so upset when told to produce factual evidence?
The problem is that anti-vaccine sentiment is NOT harmless.
Anti-vaccine sentiment means we now have diseases killing children that were effectively eradicated 20 years ago.
Anti-vaccine sentiment means that we don't have a Lyme disease vaccination because the cost of fighting anti-vaxxers exceeds the profit from selling the vaccine.
So, if we look at the balance, anti-vaccination causes real, demonstrable problems while pro-vaccination has yet to have any demonstrated factual downside.
So, yeah, we now have preventable diseases running amok because the logical community was tolerant about anti-vaccination instead of stomping the anti-vaxxers into the ground like they so richly deserved.
Not all. Some cryptocurrencies are Proof of Stake instead of Proof of Work. This means that in order to try and do a 51% attack, the attacker must have 51% of the staking coins. PoS uses magnitudes less electricity than PoW and game theory suggests it's just as, if not more, secure.
No, all, including the USD, gold or what have you are subject to P+e attacks. Currencies are consensus, and you can, in theory, bribe a majority of people to turn against that consensus at no cost.
So for instance, I could print a lot of bills and call them dollar2, and go to everyone in the world - except Bill Gates, and say:
"Hey, I have this new currency, it's the dollar2. Tell you what, I'll give you a dollar2 for every dollar you have. I'm going to do that to everyone except Bill Gates. I don't like him, so I'm going to keep half of his share of the dollar2, and burn the other half. Here's the catch, you have to commit to only recognizing dollar2 as the real currency for the next week. If I succeed, you'll be a little richer because of the deflationary effect of burning half of Bill Gate's share of dollars. If I don't succeed, you can go back to using the dollar, and I'll pay you a dollar for your trouble."
So in a very narrow, restricted way, the "rational" thing to do is to go along with this plan, and there we go, the dollar have been taken over. Obviously, such a plan would never work, but it's similar to the arguments against most proof-of-stake or even proof-of-work systems.