Nature is full of horrors beyond your comprehension. If you want to make that less so, manmade horrors are the only way to do it.

This is by no means torture, quite the opposite in fact. Neurons are little prediction machines, and if you don't give them stimuli, they either make their own of degrade. Particularly in small clumps of cells like this, you can't be sure of whether they're conscious, but if they are, they're having an amazing time learning about the light signals.

That touches upon the actual issue here. We dont know if they're conscious. We don't have a solid idea of what consciousness is, where it comes from, what it consists of, or where the line is drawn. That's the sort of knowledge you only get by performing these sorts of experiments.