I think only having "positive" reaction emotes creates a false sense of value in opinions that are generally considered bad.
If I see a post by some guy who has 100 up-votes, I will assume most people endorse his opinion. I probably won't take the time to read the dozen of pages of people completely disagreeing with him, I don't have the time to read hundred of pages per opinion. If you think down-votes are bad because they discourage debates, then I think up-votes should be removed too.
People will use emotes like "Haha" to mock others opinions anyway (including me), so why not have a dedicated emote instead of relying on emotes that can be misinterpreted by newcomers or that have a different meaning depending on context ?
Edit: I just realized I wrote an argument to support OP even though I could just up-vote him. See ? It doesn't deter debate