Marylanders actually get peed off when a person points out that slavery was legal in Maryland, which is below the Mason-Dixon line.
If they knew anything about their history, they would know that Baltimore citizens attacked Union troops passing through the city to protect DC and that Lincoln himself had to take many extra precautions when changing trains there to get to his own inauguration. They would also know the Maryland legislature was pro South and would have taken the state out of the union had Lincoln not thrown many of them in jail.