The scary idea states that it is likely that if we create self-improving AI it will consume humanity.

No, it states that we run the risk of accidentally making something that will consume (or exterminate, subvert, betray, make miserable, or otherwise Do Bad Things to) humanity, that looks perfectly safe and correct, right up until it's too late to do anything about it... and that this is the default case: the case if we don't do something extraordinary to prevent it.

This doesn't require self-improvement, and it doesn't require wiping out humanity. It just requires normal, every-day human error.