Why Do the Left Favor Mass Immigration?

To their credit, some of them don't. They understand the problems that can result from excessive immigration, especially illegal immigration. But many do, such as Ted Kennedy. Hibernia Girl, a new blog from an Irish Lass, quotes Fredo Arias - King on why mass immigration is favored:

Here's Fredo Arias-King on why the Left favors mass immigration (Arias-King heard first-hand from many U.S. Congressmen and officials why they favor mass immigration while handling foreign relations during Mexico's Vicente Fox 1999-2000 presidential campaign):
The American Left, as the Left everywhere, also has a penchant for social experimentation, even social engineering. Many leftist intellectuals and scholars often devise schemes and solutions to society’s problems, with a certain contempt for traditional ways of life. Immigration is also favorably seen by them as a way of “redistributing the world’s income” or “increasing understanding with other societies” [15] or “addressing previous injustices” or “creating better people,” etc. Some of the arguments of this group of congressmen were not too different from the logic behind the homo sovieticus, the “new Soviet man” that the communists believed they were constructing in the 1920s and 30s. Some of these congressmen used adjectives such as “happier,” “healthier,” and “harder working” to describe what their vision of the new American will be. They felt comfortable in the role of potential providers to needy groups in exchange for acquiescence in the expansion of government programs and power. They would talk to us about their plans to “guarantee health care” or “fund more services” or “give more scholarships” to the immigrants. One former U.S. cabinet member present in one of the party conventions mentioned approvingly, “What do Hispanics want? Fully-funded government programs!”Citing the negative consequences of immigration to this group is likely to backfire, as the evidence that new waves of immigrants do not perform the same as previous waves is relative good news to them. Immigration is a source of power for the étatist Left not so much because immigrants tend to vote for the party most associated with them, but because the consequences of immigration from poor countries fundamentally reinforces their argument for state intervention.I think there's also an element of divide et impera [divide and conquer] to all of this -- both in Europe and the U.S. I mean, what better way to maintain one's power than to keep the masses busy battling each other for resources and rights?

Not surprising, given the left's penchant for social engineering. With the inevitable disastrous consequences.