If you feel there is unnecessary braking going into a corner, you may only complain loudly about it (eg, "Dudes, c'mon - no brakes!") if you are within the first 10 racers in the pack. Any further back than that and it's probable that the brakes you hear squealing are not the primary offender's, but rather a secondary offender forced to slow down because the racer(s) in front of him/her has done so. Yelling at this person(s) is pointless.
Rather than whine, move to the front and show the offenders how to corner at speed properly. Your credibility quotient increases exponentially the closer you are to the front.