What would you have them use for the plural of person?
It depends on how clear you want the meaning of the statement to be. You can always add further clarifying information. "Humans" in the phrase "Humans treat animals really, really badly," could be meant to refer to "All humans" or "Some humans", but I would tend to parse it as a general statement about all humans (because in the usages that I've seen the most, if the speaker meant "some, but not all", they would've said so). Regardless, it's silly to use ambiguous wording, then act surprised when someone chooses the meaning that matches what they wanted to see or the meaning that's easiest to argue against.
Some people have a great ambition: to build something that will last, at least until they've finished building it.