Have taught to ignorant men most violent ways, (line 3)
Geez, you'd think the woman ran a rebel training camp from this description. Yeats's conservative politics come out in this line. He thinks the working classes are easily manipulated and can't be held accountable for their own actions. It's the responsibility of the higher classes to ensure that order reigns.
Had they but courage equal to desire? (line 5)
He takes another dig at the working class: they don't have the courage to follow through on the idealistic plans that Gonne imagines for them. They want to be free of the British, but they are too timid to make it happen.
That nobleness made simple as a fire, (line 7)
Yeats subtly points out that Gonne belongs to a higher class than those whom she has tried to inspire. She has a "noble" personality, like the noblemen and women of an aristocratic society. The speaker actually likes this aspect of her character, but he thinks she has abused it.
Was there another Troy for her to burn? (line 12)
The speaker questions whether Gonne is really motivated by injustice in Ireland at all. He suggests that she is out looking for something to destroy, and if it can't be Troy, then it might as well be lives and stability of the restless working class – not to mention the hearts of poor poets!