In The Merchant of Venice, is it wrong for Shylock to want revenge based on how he has been treated by Christians? If positions were reversed, would Antonio demand fulfillment of the bond...
There are two different issues at stake here. The first is whether Shakespeare would have considered Shylock justified and the second is how a contemporary reader would approach the question.
When read in original context, Shakespeare gives Shylock a wonderful speech which seems to justify his hatred of Christians ("Hath not a Jew eyes? ..."). Shylock makes a convincing argument for his being an injured party. On the other hand, much of the play is anti-Semitic, emphasizing Shylock's greed and vindictiveness in opposition to Christian charity. Thus I suspect that Shakespeare's original audience would not have considered Shylock justified and would have assumed that Antonio, a far milder character, would not have insisted on the bond being fulfilled. After all, a pound of human flesh is not of any real use to anyone.
Modern audiences, especially as we live in a post-holocaust world, are more sensitive to the plight of Jews as an oppressed minority. On the other hand, the penalty seems inhumane regardless of the person exacting it. Most modern nations have laws against "cruel and unusual" punishments; given the state of medical technology at the time in which the play is set, this would be a form of torture, something I personally consider absolutely and universally unacceptable whatever the circumstances or provocations.