Evil, in a general sense, is the opposite or absence of good. It can
be an extremely broad concept, though in everyday usage is often used
more narrowly to denote profound wickedness. It is generally seen as
taking multiple possible forms, such as the form of personal moral
evil commonly associated with the word, or impersonal natural evil (as
in the case of natural disasters or illnesses), and in religious
thought, the form of the demonic or supernatural/eternal.
Evil can denote profound immorality, but typically not without some
basis in the understanding of the human condition, where strife and
suffering [...] are the true roots of evil. In certain
religious contexts, evil has been described as a supernatural
force. Definitions of evil vary, as does the analysis of its
motives. Elements that are commonly associated with personal forms of
evil involve unbalanced behavior involving anger, revenge, fear,
hatred, psychological trauma, expediency, selfishness, ignorance,
destruction or neglect.
Evil is sometimes perceived as the dualistic antagonistic binary
opposite to good, in which good should prevail and evil should be
defeated. [...] The philosophical questions regarding good and evil
are subsumed into three major areas of study:
- Meta-ethics concerning the nature of good and evil,
- Normative ethics concerning how we ought to behave, and
- Applied ethics concerning particular moral issues.
While the term is applied to events and conditions without agency, the
forms of evil addressed in this article presume an evildoer or doers.
Now understanding the definition, I think it is easy to understand: "evil posts", "evil votes", "evil comment" are all reasonable terminologies, although they are used only rarely.
We live in a rationalist civilization, and - as also the Wikipedia page shows - this terminology deals mainly with irrationality. This is why this word is typically substituted by different euphemisms.
Evil posts are, for example:
- Intentionally misleading posts
- Posts insulting innocent users
- ...and so on.
The community bot is not capable of making moral decisions. Its downvotes are based on the flags of the users (who are), as it is described in Sonic's answer.