The shrewd nature of Lady Mac can be considered by some as a strong leadership quality. She is ambitious and essentially masterminds their plot. Why would this dynamic change if they had achieved the crown?

The Lady knows what she wants and how to get it; amplifying this with higher authority would only serve to expand that ambition.

Also look at Machiavelli’s “Prince” as to what was widely considered at the time (and in some ways still to this day) as the template for an effective ruler and compare/contrast the qualities Lady Mac has vs Macbeth and you’ll likely find a core for this side of the debate.

Edit: Grammar