I catch crappie both during pre-spawn and spawn. I prefer pre-spawn to spawn as the fish are "staging" close to shore and holding on structure which I find easy to catch. Some people like the spawn since they can toss a cork out in really shallow water and catch all the fish they want. I fish the shallow areas and if I catch a big male I usually keep them. If they are female and fat full of eggs I drop them back. It is easier to target shallow fish than deep fish so the time is ripe for all anglers, both on shore and in boat to catch crappie.
I am not sure that catching and keeping crappie in the spawn hurts the population as all fish spawn at one point or another to reproduce. If it affected the population I would think the Wildlife and Game departments would limit the catch during the season. They do studies all the time and can adjust their rules based on their findings. They have not changed any rules so I can't see where it hurts to keep them. Just my thoughts.
Good luck on catching them spawning crappie!!!