And apart from the cultural confusion icons can bring, they share with emojis the risk of a level of information density which seriously impairs legibility for readers with even relatively minor visual impairements, Text has a useful level of information redundancy - you can make sense of it when partly obscured, and a few pixels here or there rarely affect either meaning or legibility. Icons and emojis are often much less redundant, and for emojis in particular, distinguishing one meaning from another often hangs on a few pixels' difference - and if you can't resolve differences at that level, all meaning is lost.