In an idealized scenario where everyone is arguing in an attempt to seek the truth rather than to win an argument, I would agree with you. But so often, you have people linking you to whole novels that they themselves haven't even read. Does it actually contain the information they're trying to convey? They may tell you that it does, but I'm not convinced that they know it does, and all it'll do is exhaust you before you get the chance to actually address their point. The few times I've tried following through and reading these linked texts, my responses just get met with silence. The rare response you do get is not worth the extra effort required to engage with this kind of comment. At the very least, if you have someone who writes out a response in their own words, you know they're willing to take the time to actually discuss, and so you return the courtesy.