Totally agree with this. I've seen so many comments like the ones mentioned above and you're totally right, they don't start any kind of conversation, nor provide any real value to the post, they just clutter the comment section up. What's even worse is when you click through to a person's profile and see that they post that same generic comment hundreds of times (hence why they are viewed as spam). It is unfortunate.

I agree with the idea that your upvote should be your way of showing that you liked the post and a comment should be your (more than one incomplete sentence) response that is relevant to that particular post (or at least the general ideas presented in the post).

Cheers,
DE