I don't think it's backfiring. If health care has shown anything, it's that Senators respond to objective political pressure. They don't reward opponents for playing nice or punish them for being mean. Threats of refusing to cooperate over meanness are almost always a bluff.
The Democrats want to have a tough financial reform bill as an accomplishment, and they also want Republicans to oppose reform unanimously so they can show that the party is carrying water for Wall Street. The two goals are in tension. The sweet spot is for Republicans to spend several days opposing reform in a high-profile fight in which Democrats attack them as Wall Street stooges, and then cave in and make a bipartisan agreement. What I don't understand is why the GOP is letting the Democrats have the best of both worlds.