We can, however, be subject to libel for calling someone a murderer when they've not been convicted. So we have to be careful with that.
Not to mention the
immorality (IMO) of labeling someone as if they have already been found guilty of a heinous crime such as murder, child molestation, rape, etc., before the facts are known and the person has been allowed the due process of our legal system. Although imperfect it is the most fair one created by man so far. (And I won't even go into my thoughts regarding those found not guilty by a judge or jury only to have people continue to slander and libel them by referring to him/her as murderer, rapist, thief, etc.)
On the other hand, stating opinions such as someone is (or even better,
someone seems) inconsistent, sincere, sneaky, open, confusing, admirable, nonsensical, level-headed, bizarre, honest, suspicious, sweet, creepy, strong, crazy, intelligent or dishonest are pretty much subjective. I don't have a big problem with that.
JMO, The Golden Rule can be pretty helpful.