Shylock has been played for sympathy frequently in the past century. But the sense that his character fits badly in a comedy is an old one. Already in 1709, Nicholas Rowe wrote, “Tho’ we have seen that Play Receiv’d and Acted as a Comedy, and the Part of the Jew performed by an Excellent Comedian, yet I cannot but think it was design’d Tragically by the Author. There appears in it such a deadly Spirit of Revenge, such a savage Fierceness and Fellness, and such a bloody designation of Cruelty and Mischief, as cannot agree either with the Stile or Characters of Comedy.”
Quoted in The Merchant of Venice (Shakespeare: The Critical Tradition) 