Dear.. I believe no one should ever go against the topic until and unless it ends with a question mark. Look, essays topic is a phrase or a statement that sums up ur essay in the fewest possible words. If the statement of the essay says one thing and the body contradicts it, it would make no sense at all. However, in case the statement is a question then you have both options: going against it, or justifying it. I hope it makes some sense to you.