So do I. You already said it: The forum has a multi-quote feature. Please use it.
If that means that a post cannot be (dis)agreed upon anymore with a simple reaction so be it. You have a keyboard. Use it.
Just to be clear, I don't think I've said anything against combining messages and using the multi-quote. And I very much support the idea of using the keyboard instead of reactions, with the possible exception of replacing "me too" messages with agrees or likes.
As mentioned, this behaviour is against the CoC. If you encounter such a thing please report it so we can investigate.
How does one report a reaction? Click Report on the message that was reacted upon?