Insight and incite are pronounced exactly the same, but the meaning is very different. Let’s take a look at how we can play with this difference to make a joke.
His speech was extremely insightful!
It was an intelligent, thoughtful, perceptive analysis. It showed insight—deep understanding of the topic.
His speech was extremely inciteful! It encouraged the crowd to riot.
Yikes!
To incite is to provoke or stimulate or stir up (usually to violence or other bad acts). The inciteful speech riled up, triggered, inflamed or aroused the audience to do violent or unlawful behavior.
Inciteful is a real word, but not used often. You will probably only see it used to create a play on words, a joke that takes advantage of two different words that sound the same. I can imagine a witty newspaper headline: Another Inciteful Speech from Candidate X. But readers would realize that 1) the writer meant to use the word as a joke and 2) the content of the speech did not show deep understanding (insight). Instead, it triggered the audience to act on their grievances.
So, what if you really wanted to say the speech promoted violent acts?
You could say
The speech incited a riot. [Using the verb form, to incite, is more common usage.]
You could say
The speech was incendiary, explosive, or inflammatory. [All these words bring up images of fire and eruption. The speaker’s words caused emotions to explode into actions (bad ones).]
Or you could say
The speech was dissentious [stirring up dissent/ contention], or rabble-rousing [stirring up the grievances or prejudices of the listeners].
To say the candidate knew what he was talking about? Use insightful.