Your UK investing forum members have a common interest, much like a cat or Morris Minor fancier's forum do*. For a forum with such wide ranging topics as this one does there is bound to be some / a lot of discord (not the social media site) and downright infighting, especially given the diverse backgrounds of the members, and the ages of most (dare I mention the grumpy old man syndrome?) The very fact that this thread, designed to receive suggestions on cutting down toxicity and negativity, has descended into a pit of toxic negativity on just about every page, would suggest that a firm hand is needed by the moderation team to keep things civil and on topic. It's rather like the head of an asylum asking the inmates if they're sane enough to be released into society and, while a few say yes, we are, thank you, the majority carry on gibbering and flinging excrement at the walls, the asylum head, and the other inmates. That doesn't mean I'm calling for the same (often overly, in my opinion) heavy handed policing as previously though. Maybe a walled off section where those who enjoy a bit of faeces flinging and receiving can retire to when the will takes them and have at it. You know who you are.
Regarding the emoji question, I'm in favour of them. On other fora I've visited that don't have them, you often get a post made followed by a dozen saying "good post", or similar, or the opposite, followed by a dozen more for each of those agreeing or disagreeing with them, so you wade through pages of the stuff until you get to another original post. They do seem over complicated here though. Simple like and dislike ones should suffice - though "groan" and "that's been posted before. Multiple times" ones would be nice for the joke threads.
*Though my experiences with some common interest fora shows that they too can often erupt into clique warfare, reinforcing my point about firm moderation.