I think the argument is that, to the uninitiated, x = x + 2 looks more like an invalid equality than "replace the value stored in x with its current value plus

I think the argument is that, to the uninitiated, x = x + 2 looks more like an invalid equality than "replace the value stored in x with its current value plus 2". Personally, it seems to me that = for assignment is so ubiquitous that this argument has become stale. I still use the arrow because it's the prevailing recommendation in R style guides.