What's wrong with accumulators? They are useful for transforming head-recursive code into tail-recursive code.
Granted, accumulators can't really improve code that traverses trees. But for code that traverses lists, like zip... accumulators can be useful. Also, the added complexity isn't too bad.
In Okasaki's _Purely Functional Data Structures_, he adds an accumulator variable to the binary (and RB, etc.) tree membership test as an optimization, because it turns the test from up to 2*depth time to constant depth+1 time. (It's exercise 2.2.)
I suspect what the post meant was that while accumulators certainly have their benefits, reflexively using them everywhere is probably a sign that you don't really understand them.
Granted, accumulators can't really improve code that traverses trees. But for code that traverses lists, like zip... accumulators can be useful. Also, the added complexity isn't too bad.