Well, renewing them for the middle class is a good idea but letting the cuts expire for the top earners will get $750 Billion back into the treasury. And the reasons the right claims for extending those are simply not true.
If you own a small business and file 1040 Schedule C, the income of the business is entered, then the expenses, including payroll, are SUBTRACTED. The net, the amount you keep for yourself, flows to form 1040. With the expiration of the tax cut for incomes over $250,000, only that portion you pay yourself over that number gets an additional 3% tax. So, if you pay yourself $300,000, your tax liability goes up $1,500 (3% of $50,000), about one-half of one percent of your whole income.
Those who claim it will hurt hiring are lying through their teeth.