I guess to me, unless you have something like the weird system Reddit uses, you either click like, or type something like "this is a great post." Or "thanks!" Which is basically the same as using the reactions, but creates a bunch of spam. If you have to write more than that to interact with anyone's posts, tons of posts would go essentially ignored because people only have time for so many thought out posts every day.
I agree that if you want to disagree with someone that more detail is better because just downvoting or thumbs downing someone is just throwing negativity out there to be misinterpreted as the owner sees fit, and would discourage people from posting a lot more than not getting as many likes as someone else.
I don't see how throwing low detail positive reactions is remotely a bad thing though. I don't always feel like I can add something more than someone else already said (better than me), or I simply don't have time (probably rich coming from someone like me who posts too much). But, I still want to throw a quick smile, agreement, thanks, or laugh someone's way to let them know I appreciate it.