I'd rather have the buttons than 10 posts in a row that just say the word "agreed" and then having to weed them all out for the real responses.
I'd be opposed to adding negatives such as disagree, dislike, thumbs down icons, etc. If someone disagrees with a post, the right thing to do would be to post a response with *why* they disagree, and thumbs down is just rude, and based on how it's used on YouTube and other similar sites, it's typically used to troll and be obnoxious.
I personally don't view the use of "prayers" or "funny" as goading, even if it's because a person disagrees with me, provided they are not overused and used maliciously on every post someone makes. Sometimes people just say the craziest things and you can't help but laugh or say a prayer rather than getting upset or angry.