Harlow's experiments: Cruel or necessary?

I think that everyone will agree that taking a baby monkey away from their mom and subjecting it to scary things is cruel but then again, it is also very important to the study how humans react to such things. While using a human is out of the question why is it okay for another type of primate to suffer instead? While curing depression and figuring out how environment effects development could help our species, is it worth the sacrifice of all those monkey babies that grew up with wire mothers? I guess the main point of this blog is really to answer the simple question of whether years of animal suffering now worth a future without these problems in our societies future? And where is the line that separates justifiable from unforgivable? Or is there even one? The jury is still out for me so far, while I agree that it is cruel and something that is nowhere near the 'good' end of the moral scale, the research itself can be very beneficial in the future and I'm not sure where a line can be draw if there even is one.