I feel the Not So Different trope only really works when the hero and villain actually do share a few things common.

Most of the time the hero calls them out on their bullshit but if they believe it, there will be a point where the hero realizes they are not alike.
Alternatively, the villian is saying that vigilante and criminal alike are chased by the police. To join his side because the law sees them both as a menace and that his good will with the people will dry out if he makes any mistake.