Leaving aside that this is about "much of Manhattan" rather than "all of Manhattan" it remains that Manhattan, Brooklyn, New York City in general are well known as one of the larger jewish neighbourhoods on the planet.
Jews comprise approximately 10% of New York City's population, making the Jewish community the largest in the world outside of Israel.
Some of your other what if's are addressed in the article, if you're a good faith commenter looking for actual serious issues then there's also 100 years of existence in Manhattan and the wider New York City to draw upon.
Perhaps you could highlight some actual real issues that have cropped up in the last century?