Yes, if computation were free, then you wouldn't need genetic algorithms at all. But remember that this is a huge, huge "if" that none of us will ever live to see!
Still, since you're asking... if computation were infinitely fast, there would be no reason whatsoever not to apply the simplest brute-force combinatorial generate-and-test sledgehammer to a problem. Every question that can be answered with a finite set of information (i.e. a constraint satisfaction problem in the loosest possible sense of that term, which is quite loose indeed) would be instantly solvable; hill climbing, heuristics and all the clever simplifications that we now use to build e.g. a world-class chess engine would simply not be necessary.
Put another way, if computation approaches infinite speed, the decision which approach to use becomes founded on how hard it is to write the computer program to be executed, not how long it takes to actually execute; and that means that it simply isn't worthwhile to invent a more complicated algorithm when the simplest possible will also work and run in the same time.
Arguably, computation has indeed been moving in this direction, but again, remember, that we aren't quite there yet, and probably never will be. (Unless the quantum computer is perfected, of course.)