There is nothing wrong or unethical about lending with interest. It is a common practice which is done in all civilized law-abiding societies.
Still, the Torah expects of us to treat all our fellow Jews as family--and when a family-member asks for a loan we don't charge interest. As the verse says (Deuteronomy 23:20),
"You shall not cause your brother to take interest."
As far as your second point, that Jews are associated historically with being moneylenders, I'll repeat what I said in the comments.
As ShmuelBrin correctly pointed out, Jews in Europe were barred from most other professions at many times throughout history. One of the only available jobs left to them was moneylending. The fact is that historically, the Christians followed the Torah's prohibition against lending with interest to ones "brother"; but to the Christian, "your brother" is the Christian! So Christians could not charge interest rates to each other, so the Jew became a moneylender to fill that gap.
Shakespeare's Merchant of Venice is just another example of simple anti-semitism (despite the "sympathetic reading" that Wikipedia brings, with no sources). From fff.org:
In medieval Europe, many governments restricted money handling and money lending to Jews and Arabs, believing them to be practices morally inappropriate for Christians. Entry into many fields was barred to Jews. Those who were competent financiers were most likely to succeed in a society where they were essentially personae non gratae.
Also, since Jews were constantly being expelled from this country or that one:
The need to flee at a moment's notice made it a bad idea to keep whatever they had accumulated in immobile forms, and more sensible to have it in gold or jewelry.
From this perspective, it's quite easy to see how the anti-semitic stereotype of Jews being greedy, miserly, opportunistic and cunning moneyhandlers etc. came to be.
As I mentioned in the comments, it's quite interesting to note that since Jews had been completely expelled from England 300 years prior to the writing of The Merchant of Venice, it is quite likely that Shakespeare, as well as the average Englishman, had never met a Jew in his life.