It's not justifying cruelty. It's acknowledging that it is a cruel activity, but chose to look away when it suits us. As I do. There is no way to justify torture, but we can accept it. We can accept that we just don't care enough about the animals. That we don't empathize enough with them.
People who try to justify animal experimentation on some moral grounds are the worst hypocrites of all in this issue. Those to who try to devalue animals worth, at the same time elevating ours. It's like a bully on a playground. Nobody can stop the bully from taking the sweets from the smaller kid. From that reaching the conclusion that it is right for the bully to take the sweets is just offensive.
Even so, I'm still all for animal experimentation. I'm a greedy crud who'd rather not suffer later in my life from debilitating diseases I'm genetically inclined for. Better them than me.