What advantage do free swimming larvae provide for the echinoderms?

I believe the free-swimming larvae can travel much greater distances than the bottom-dwelling adults, increasing their range. If the environmental conditions for the adults become bad, the larvae to another area that may be favorable. An echinoderm is a sea animal that has a hard spiny shell, or exoskeleton. Echinoderms display radial symmetry, having five similar body extensions from a central point. 

Yes he thought they should be left to chance why, because he thought that was the best thing to do