I'm gonna agree completely. If you're concerned about having reliable brakes (and you damn well should be), then you should use them as they were intended. Grinding out the MTB levers sounds really dangerous. Clamps are made to precise tolerances to fit specific sizes and shapes of handlebars. If your brake clamp is not perfectly round, there will not be sufficient contact area to effectively grip the handlebar. A disaster waiting to happen.

Just because you think certain parts "should" be interchangeable doesn't mean they are. Perhaps on some abstract level it would be great to be able to swap parts with reckless abandon. However there are many good reasons why some parts don't work with other parts. A number of people have already pointed out reasons why MTB brakes are designed differently from road brakes. I'll add one: mountain bikes generally have V-brakes, which have a greater mechanical advantage than caliper road brakes, which produces a greater stopping power per unit cable travel. These require correspondingly different levers.