>It is impossible to build any website that cannot be taken down

This is becoming less true each day, especially with the advent of IPFS and Ethereum. Uniswap's website will never go down. uniswap.org might be seized but uniswap.eth cannot be altered by anyone.

In a few decades it will be normal for websites to be decentralized and permanent. It's actually quite needed for the robustness of critical internet architecture.

I am not sure about IPFS but didn't Ethereum have a 51% attack last year?

No. You are probably thinking about Ethereum Classic which has been 51% attacked a few times.

This sounds like a problem to solve.

How? Even if you were to host a website on a satellite the government could launch a rocket and blow it up. If the website is hosted on Earth they could physically cut cables if they wanted to. There is no way to fully prevent the government from preventing access to a website. The internet is decentralized, but not fully immune from governments.

I mean, you can have more than one copy of the website. Maybe a government can send one satellite-destroying missile, but probably not thousands of them.

Think about how many people have the Linux kernel Git repo cloned on their workstation. It would be essentially impossible for any government to destroy all copies.