It's a complicated text, but it seems clear to me that a straight reading of it makes it a comedy with Antonio as the lead and Shylock the antagonist who meets his comeuppance at the end. And remarkably, we have contemporary stagings that play it that way still. (The Michael Radford movie, with Jeremy Irons flirting with Bassanio, toying with Shylock with a handsome smile on his face, skipping through the movie as if nothing can touch him, hits way too many of those notes for me.) The problem with Merchant is that Shakespeare was too smart, too clever to create a mere stock villain. Shylock is too alive to serve the role the drama designates for him.