> arr[n:m]

arr[n..=m]

> arr[1:m] and arr[(m+1):end]

arr[0..m], arr[m..]

Much nicer.

> Arrays are (conceptually) not pointer arithmetic.

Look at a ruler. Does it start at 1?

This is such a classic example of online discourse in general. There are two options, and folks tribally cling to one or the other without realizing that both are legitimate and well-suited for different situations.

Yes, of course distances are measured starting from 0. But we count discrete things starting at 1. You can do mental gymnastics to enumerate from zero and many programmers are (unfortunately IMO) taught to do so. It's a hard thing to learn that way, so for the folks that have done so, it often becomes a point of pride and a shibboleth.

As a classic example, a four story building has four floors. But you only need to go up three flights to get to the top. You can legitimately call the top floor either 3 or 4, and folks are similarly tribal about their own cultural norms around this one, too.