Based on how Christians treated him, is it wrong for Shylock to take revenge on them? In reversed positions, would Antonio demand fulfillment of the bond according to the set terms?
Shylock certainly has good reason to be bitter, but it does not follow that he is therefore right to seek to cut out a pound of Antonio's flesh. There is good evidence Antonio would not do the same.
First, about Shylock's bitterness. It is obvious the Gentile characters all share anti-Semitic assumptions. Shylock is often referred to as "Jew," in context clearly used as a racial slur. Elsewhere, the characters attribute Shylock's evil character to his being a Jew. His daughter Jessica has a very different character, causing characters to speculate her mother must have committed adultery with a Gentile. Incredibly, Jessica does not even argue the injustice of this. In Act I, Scene 3, when Shylock accuses Antonio of regularly spitting on him and calling him a dog, Antonio does not deny it, but responds, "I am as like to call thee so again,/To spit on thee again, and spurn thee too." This is the only time in the play that we see Antonio say anything unkind to anyone.
Looking at all this, it is clear Shylock has lived his life as a member of a hated minority. As he points out in Act III, Scene 1, "If a Jew wrong a Christian, what is his humility? Revenge." This is undoubtedly true. So in one sense, Shylock is only doing what has been done to him or what would many Gentiles would do to him if given the opportunity.
There is, however, a paradox about bitterness and revenge. No matter how justified, they are always ugly. What Shylock wants to do to Antonio is not really justified by what Antonio has done to him.
Antonio says Shylock hates him primarily because Antonio often covers the debts of those who borrow from Shylock and find themselves facing high interest. If this happens many times, it is easy to see how Shylock could come to see Antonio as a bitter enemy always trying to ruin him; however, rescuing people from a loan shark is not a crime deserving of death. It seems that Shylock has transferred all his bitterness and frustration against all Gentiles — and indeed, his bitterness over every single time things have gone wrong for him — to a single person: Antonio.
Thus, what Shylock wants is all out of proportion to what Antonio owes him. He does not just want his money back. He does not just want back ten times the money that Antonio owes him (which would, arguably, repay him for the interest he might have made if Antonio hadn't rescued Shylock's debtors). He does not want Antonio publicly sued for slander, or made to apologize, or anything like that; he wants blood. Shylock is entitled to apologies and perhaps payments for the way he has been treated, but after being insulted for so long, his desire for justice has morphed into a desire for bloody revenge.
There is no evidence that Antonio ever desired to take a pound of Shylock's flesh or that he would ever draw up an agreement with that possibility in it. In fact, when given an opportunity to ruin Shylock, Antonio asks the Duke to let Shylock keep half his wealth after Shylock says he might as well die if all his wealth is taken from him (Act IV, Scene 1).