I kind of get both sides. It's like any pet, and I have tons of all kinds. If you just "throw" them together you're gonna end up with fights and aggression, but if you are too cautious and try to "acclimate" them too much and don't allow natural behaviors, it can cause aggression in a completely different way. For example, I have a lot of dogs, when we get a new one we spend a good few days to a week introducing them and giving them time to get to know each other before they are left alone, to prevent anyone from getting hurt. Though, you gotta let them growl at each other, nip and bear teeth, or at least show their dislike/unhappiness in their natural way, or they end up with complexes that make them more aggressive without warning signs. Now they all get along really well, though we get growing from time to time, they also know how to respect each other's space/boundaries/etc.
In some ways, you do I think need to at least give them time, or the right setup to have a chance to get to know each other safely, but at some point, you do need to let them just figure it out on their own.
Think about it this way, what if you were upset with someone that you were forced to share a room with; you were yelling at them telling them not to steal your stuff and invading your space. But whoever put you in this room keeps getting in trouble for "yelling" or "showing aggression", and you keep getting put in a box for it. Would you feel that is any more morally ethical?