People should be able to use reactions freely on whatever posts they please.
Obviously you really shouldn't go around "angry facing" a members posts just because you didn't like one thing they said, but in that case it just shows their immaturity. And if they don't like something they should simply scroll past. Same goes for everyone else.
Using the angry emoji doesn't always mean it's directed at the member who's post received the reaction, I will sometimes use it when someone posts about something bad that had happened to them or their pets.
But no matter how people use it, it's up to you to decide how you react to it.
At the end of the day, these silly little "reactions" mean nothing. They can't actually effect you. So there's no reason for someone to get offended or cause a big deal over any of them.