Having something that can move to self-center is not a problem, but leaving a piece that's supposed to be tight loose on purpose is not the way to do it. If you've seen the slide pins that a car's disc brake rides on you can imagine the force they deal with. They're usually a half inch or more in diameter, machined perfectly smooth, greased, and sealed with boots against the elements. That's a far cry from two loose 5mm bolts 'kinda snug' and a rusty piece of sheet metal backing plate for them to slide on.
Tightened up, those fasteners can support a lot of force but they are not designed to handle it while sliding around sloppy like that. Further, if you get into a harmonic oscillation the brake could shudder violently, damaging parts, make the bike unsteady, or even lock. It's a very bad idea.
Scott