[harrygallagher4]

(note: everything I'm about to say is just my take on early CS stuff, I don't know Dijkstra or how he thought, these are just conclusions I've personally drawn from reading about the history of computing)

I think it's hard to imagine because it comes from the mindset of those who pioneered programming, like Dijkstra. You're right that he seemed to be concerned about the 'purity' of the process. It's clear from reading the original article that he (and others) thought about programming in a much more 'mathematical' way than modern people. Dijkstra wanted a program to be clearly defined and computable all the way through, but when you're jumping around the code arbitrarily that's... difficult. All of this comes from the fact that computing was birthed from mathematics, and the people involved in it back then were more likely to have a base in math.