Smart / dumb are relative scales, so there will always be smarter, and dumber, no matter what you do. If you filled a society with what we currently define as genius level intellects, there would be the equivalent to dumb people amongst them - the dumb people would have 145 IQ's and the smart people would have 180 IQ's --- you get the idea.
Majority rules will always allow one group to optionally eat the other, and violate the rights of the minority. Whether that minority is the dumber 49% or the smarter 49%, either scenario is equally morally reprehensible.
Peikoff would say: think in extrapolated principles. Look up the first serious conversations Peikoff had with Rand (she couldn't get him to think in principles). Whether you're dealing with smart people with 250 IQ's, and 'dumb' people with 160 IQ's, the smart people might decide they know what's best for the 'dumb' people (and proceed to violate their liberty). The principle remains whether you're dealing with 70 IQ's and 160 IQ's or much higher scales of intellect.