While that argument makes the alarmist blogs and MSNBC, it neglects that, everything else being equal, if hurricanes are becoming rainier, they must be getting stronger, as the fuel that drives the kinetic whirl of the tropical cyclone is the heat released by the condensation of water.
The consequent condensation of the water vapour it is carrying heats the air further (the change of state from gas to liquid sheds latent heat), causing it to continue rising.
Without such particles, clouds would be rare: the air would need to be freakishly saturated with water vapour or strangely cold for condensation to occur.