Under what definition of easy? If it's easy to stop, then why don't the people signing the letter just do it, rather than trying to appeal to others to do it instead?
Aligning thousands of people (all of the people with the knowledge and resources to move forward quickly), with no dissenters, (as a single dissenter could move things forward), to a common goal is not easy. It's effectively impossible.
If one of the many close calls had gone a little differently and a city were nuked accidentally, it would cause a global outcry and there would be yet another international effort to reduce the global nuclear stockpile to zero. And there’s a very good chance it would succeed. At the very start there was actually an agreement to not initiate a nuclear arms race but the Russians went back on it. So, for something that is “impossible”, we seem to see signs of it all the time.
The reason you think it’s impossible is because most things aren’t like this. Most things benefit some people and harm other people. This harms all people. Be a part of the solution instead of dismissing real solutions when you have no logical reason for doing so.
That's up for debate. I personally think AGI will be good, though not with a level of certainty that would allow me to use it as an axiom in a conversation.
> The reason you think it’s impossible is because most things aren’t like this
The reason I think it's impossible is because there are several other things like this and we did the same thing. When there is massive benefit to dissenters, getting everyone on board fails. Nukes, fossil fuels, deforestation, industrial chemical controls, overfishing, etc. are all examples of how we continue to fail at the exact same task.