Shylock's Humanity in Shakespeare's The Merchant of Venice

DA Traversi writes that Shylock "is among the first of Shakespeare's characters to require from us, like so many of the later tragic heroes, a response in which different and even contradictory judgments are simultaneously evoked". He is in many ways unchanging - something of a stock character, a distillation of the Jew as represented in the literature of the time, such as the Jew of Malta. But where Shylock differs from Barabas is in the characters motivation for violent action, which must, in context of the play, be seen in some ways as outside a strictly condemned Jew. In fact, it is this very sense of motivation that sets Shylock apart from Barabas, for in writing on Shylock’s reasons for his actions, an audience is given the chance to understand him, and in some slight ways, perhaps, sympathize with him. Traversi echoes this sentiment when he writes that Shakespeare “provides [Shylock] with motivation for the behavior expected of him in the light of established conventions. Once more a growth in expressive capacity is accompanied by a widening in the possibilities of dramatic representation”.
Shylock is not a likeable character. Not in Shakespeare's time, and not in ours. A reader is struck by the many ways in which Shylock withholds - from his very first lines we can see that he is devising a private plan while doing business with Bassanio; we see him make an aside to the audience which reveals his hatred for Antonio, without Bassanio’s knowledge; further and perhaps most importantly, we learn that his fortune is made by withholding money, in a sense - by the practice of usury. We are automatically made to view him askance. And yet, within this negativity Shakespeare plants his first seeds of a human within Shylock’s persona:

I hate him for he is a Christian,
But more for that in low simplicity
He lends out money gratis and brings down
The rate of usance here with us in Venice.
...
He hates our sacred nation, and he rails,
Even there where merchants most do congregate,
On me, my bargains, and my well-won thrift... (Act I, S.3, 42-50)