Shaka has absolutely no idea what he is talking about on this topic. (Though seems like a good guy otherwise). His opinion is not terribly uncommon on this board but completely wrong among all those with the same view in my opinion.
There are many means of weight and weight distribution for scuba diving. Some use weight belts, integrated systems, some distribute via a back-plate, tank weights, and several others. Ankle weights are just another tool in the toolbox.
If you have back trouble for example ankle weights are an excellent means to distribute some of the necessary weight. Some people have floaty feet. In many cases this can be addressed with tank position changes but not in all cases.
The detractors use words like "hydrostatic instability", "increased exertion", and "increased SAC rate". While this is true in a test tube, it's completely irrelevant to real world diving. If you were to do dive #1 with 20 lbs in a weight belt, then dive #2 with 15 lbs on a weight belt and 5lbs in ankle weights, you would not find a measurable difference.
I do some dives with ankle weights and some without depending upon my weight needs for a given dive. (Changes based on what type of gear/dive I am doing).
--Matt