Even characters with good intentions can become the antagonist in a story. To understand why, let's define antagonist.
a person who is opposed to, struggles against, or competes with another; opponent; adversary.
the adversary of the hero or protagonist of a drama or other literary work:
Iago is the antagonist of Othello.
We can see from the above that an antagonist is someone who struggles against another, someone who opposes them. This we likely already knew. There is a second layer to the meaning of the word antagonist, and that is as it applies to writing. An antagonist, if the term is looked upon as a writing tool, is the person who makes things happen to the protagonist. Someone who puts in motion a chain of events that changes the situation or personality of the protagonist and instigates a story.
Well meaning characters are capable of performing the function of antagonist just as well, or some times even more effectively, than a character whose intentions are harmful.
For example, in an episode of Friends - the episode entitled The One With The Free Porn - Monica attempts to live vicariously through Ross by encouraging him to live out her fantasy of falling in love with someone from a foreign land and confessing that love at the airport before they depart for their home country. Her constant reassurance that everything will go as she fantasizes causes Ross to go to great lengths to live out Monica's fantasy and chase Emily to the airport to confess his love. When he finally tells Emily how he feels, she doesn't say it back, and Ross is crushed. Despite Monica's best intentions, Ross was pushed into conflict because of her meddling. She was the antagonist of his story for that episode.
When we put antagonists into a box, we run the risk of developing flat, predictable characters that aren't as effective as instigators and aren't believable as human beings. To understand that is to know that we must look for new ways to use the antagonist tool and create different modes of transportation for our conflicts. Making use of a well meaning, likable character as a mode of conflict and a working antagonist is a great way to refresh our stories and create new angles to entice the reader.
Create 3 well meaning, likable characters with flaws that create conflict and antagonize the people around them. Use them in a short narrative to describe a situation where a protagonist character is thrown into turmoil at the hands of an antagonist who never meant any harm.
What do you notice about writing this kind of character? What was difficult about it for you?