It seems wrong for any social media platform to have a like/heart button without a dislike/evil button. Does not allow symmetric expression of opinion and allows for manipulation

Information symmetry is important for democracy (and which is why self censorship of even the stupidest opinions should be very carefully considered) but so is expression symmetry.

YouTube has a thumbs down option and I have seen it put to good use. On the other hand I have seen the option of @Twitter being completely misused (based on my interpretation of what stands for)