Everybody knows that you don't raise taxes during a recession. And letting the Bush tax cuts expire is the same as raising taxes. Here's a good article for you to read glasspilot that actually comes from Yahoo, which I would consider left leaning. Raising anybody's taxes is robbery, especially right now.
http://news.yahoo.com/s/ap/20100916/ap_on_bi_ge/us_tax_cuts
http://news.yahoo.com/s/ap/20100916/ap_on_bi_ge/us_tax_cuts