I mean, if Doctor Evil suddenly decided to spend tens of billions of dollars to destroy the three main credit card networks, he could probably do it. In fact, it might be easier and cheaper than attempting to degrade or bring down a distributed block chain network. The credit card networks are built upon many layers of ancient, pre-Internet technology, full of discoverable vulnerabilities and critical points-of-failure.

But we all know that it wouldn't happen. Doctor Evil would never want to do so, because even him, the most evil person in the world, would still want to be able to use his credit cards to eat out, go to the movies, and order stuff online. Also, he would never want to do something that would make him enemy #1 of every other person in the planet, including every other super-criminal!

What Doctor Evil actually wants to be able to do is figure out ways to steal or get balances from participants in the network without destroying the network: steal poorly protected wallets, hack into poorly secured exchanges, find ways to get blackmail payments on the network (e.g., by launching DoS attacks on the web), etc. The network itself is too useful to everyone for anyone to want to destroy it.

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PS. For the record: I have no economic connection to Algorand the block chain nor to Algorand the company, but I'm (superficially) familiar with some of Silvio Micali's past work and also, I know one of the company's top executives. In my judgement, the Algorand block chain has great technology, and Algorand the company has really great people. Their main challenge, as I see it, is overcoming the powerful network effects already accruing to other block chains.