Just a silly quick question: why isn't right-recursion a similar problem?
Very roughly:
Left recursion is: let foo n = n + foo n in ...
Right recursion is: let foo 1 = 1; foo n = n + foo (n - 1) in ...
In short, matching the tokens before the right recursion will constitute an end condition that will stop infinite recursion --- if only because you'll hit the end of the input. Left recursion doesn't consume anything, just re-executes itself.