This stuff used to bother me but then I observed nature and its cruel rules for long enough, and I realized that suffering is one of the few constants in life, one of the guarantees. Wasps that paralyze spiders for months so they can be eaten alive by their offspring, bird species where most chicks are left to stave to death, etc... yeah nature is just as cruel as humans can be, but at a much larger scale in perpetuity, and we're a lot more efficient at turning that suffering into greater good that lessens the suffering of others in perpetuity. So, while I don't condone or even like to think about baby monkey experiments, I will not bat an eye at lab mice being given Parkinson's so we can observe and seek answers and cures.