Also, whats wrong with using flaps to slow down...
Flaps: Used to increase the lift coefficient of the wing so you can fly more slowly.
Speedbrakes: Used to increase drag.
Yes, the last few stages of flap, normally used for landing, are there to produce extra drag as well as a bit more lift. Going from clean to the first stage of flap on a 737 is not really going to help much if you want to lose energy as the wing is still fairly efficient in that configuration. What it will do is stress the airframe more than usual, make the ride worse by lowering the wing loading and require a larger pitch change to stay on the same glidepath. Plus, when you're flying at limiting speeds, all it takes is a gust or positive shear and you've got an exceedance, which is generally taken quite seriously with flaps as the aerodynamic loads increase very rapidly with airspeed.
If you're too high and/or fast, use the speedbrakes; if that still isn't enough, drop the gear as that is much tougher (built to withstand landings like mine!). If you're *really* high, slow down to landing speed, deploying the flaps on the normal schedule - when you're configured, you can do >1,000' per mile.