Why doesn't ProZ.com set a minimum rate for translation?

At times, the suggestion has been made that site staff institute some form of technical mechanism to dictate minimums. Although ProZ.com has instituted certain mechanisms which may help to stabilize rates (see FAQ on rates), ProZ.com has no intention of instituting a minimum rate mechanism in the near future, for the following reason:

We believe that each member should be entitled to set his or her own minimum rates. We provide a rates calculator to assist site users in making the necessary considerations, and provide optional filters so that in effect, a site user can set his/her own minimum rate. This is in line with the site's philosophy of not interfering in members' businesses.

If that is not reason enough, consider that:

Even if it were conceptually possible and advisable to set a minimum rate, we would not currently have a means of enforcing it.
Whether attempting to set a minimum is legal or not is an open question, and not one on which we have had adequate advice (comments from lawyers are welcome)
Other sites have attempted to set minimum rates, with no apparent effect.

It is in the interest of translators, and ProZ.com, for rates charged to be consistent with the demands of our challenging profession. To that end, ProZ.com's staff has welcomed and encouraged legal communication and cooperation among translators. But we believe that control of rates does (and should!) reside in the hands of service providers.