I know that a few users do abuse this feature - I think all of us have gotten annoying mails from someone or the other who chose to do a "Reply All" instead of using his/her common sense.
But having such a drastic solution for this problem creates more problems than it solves. It handicaps users who have to do a legitimate "Reply All" for work related mails. (Or even when you have to reply to say 5 out of the 7 people on the mail thread - doing a Reply to All and then removing the extra 2 folks is much easier than pasting everyone's email ID again).
But, fortunately, there is a workaround. You can't enable the "Reply To All" button. But you can create a new button that does exactly the same thing as that one.
Read the post below. I have tried it myself, and it works!!
Link: Neil Mitchell's Haskell Blog: Enabling Reply To All in Outlook