There's a good reason for that opposition, which is the cost a temporary fix would impose on anyone responsible for dealing with payroll taxes:
"People need to realize what the Senate did, and kind of in a hasty way, they did something that is going to cause a lot of problems. By only extending the tax cut for 60 days, that's going to cause a lot of problems mechanically for businesses to implement it," the 57-year-old Mr. Gibbs said.
Employers who file tax paperwork on a quarterly basis, he said, will have to fill out payroll withholding forms twice, he said. "At least they should have made it for 90 days for the quarter. It's not workable."
The Senate over the weekend approved a bipartisan compromise, backed by President Obama, to extend the payroll-tax cut for just two months, while the GOP-dominated House approved its own bill for a 12-month extension. The tax cut will expire Jan. 1 if the two chambers cannot reach an agreement.
Emphasis mine. The Gibbs quoted here is a Republican congressman from Ohio, by the way. What he's saying is true -- payroll withholding is done on a quarterly basis and if the rates change, that means a lot of extra work recalculating things. For a small business, the time spent dealing with a midstream change is time they will not spend on their business. It might not seem like much, but in the aggregate such things add up.
As always, the problem is that (a) Republicans are terrible at explaining things; and (b) even if they explain things competently, there's an even money chance the MSM will not let the message get across. And taken together, (a) and (b) are why so many of us blog.