To improve our way of expressing ideas of course. Imagine throwing a sarcastic comment here in plain text, others might get offended isn't it? But with the power of grin/tongue emoji, your comment would look more funny thus others can easily ride with it . (Now read my post without a single smiley. It sounds like a preacher, right? I hope you get it.)

I think the emoji and icon itself is not the main problem, an abusive user is. So whether we only had one or hundreds of emojis available, it doesn't matter. The decency and neatness of one's post still depends on how he will use it.