because that is the most effective way to satisfy almost any possible goal function
Perhaps more accurate: because that is a likely side effect of the most effective way (etc.).
Not a side effect. The most effective way is to consume the entire cosmic commons just in case all that computation finds a better way. We have our own ideas about what we'd like to do with the cosmic commons, and we might not like the AI doing that; we might even act to try and prevent it or slow it down in some way. Therefore killing us all ASAP is a convergent instrumental goal.
Following some somewhat misleading articles quoting me, I thought I’d present the top 9 myths about the AI risk thesis: