I'm agnostic about whether ASI is possible. I don't have a dog in this fight other than a pro-human bias. I have used coding agents as well and I'm certainly aware that they are limited (at least in my domain).

I think the main argument for ASI is something like (i) extrapolating the progress from the past 10 years into the future, (ii) rapid progress apparently still being made, and (iii) seeing no obvious theoretical limitations.