There is nothing wrong with using the emojis as long as it's not used as an personal attack mechanism.
The laughing emoji is positive and fun when it's used by someone sharing in the joke. The OP made them laugh! It's not fun when it's used to belittlingly laugh at someone's serious comment. One might get points for quoting the comment and saying, "That is/You are stupid." but they can say the same thing safely with the laughing emoji. The angry emoji can also be both positive and negative. It's a positive emoji used when people are supportive and angry for you or angry with you. It's not positive or supportive when it's used to oppose what the person said. While one won't get points for saying, "I disagree with everything you just said.", I don't think it's much of a conversation to convey that thought with an emoji.
I actually think it's perfectly OK to use the emojis in both ways. However, the excessive use of the negative emojis by one poster against a single poster (or group of posters) on a thread moves from a simple, quick reaction into personal attack category. LilyWDW used 9 negative emojis on DisneylandFreak's comments with 6 in the space of 4 minutes. All of the negative emojis by Lily were directed at DisneylandFreak.
I commented because I have seen her do it others and she has done it to me in the past.
.
