Forgiven debt is taxed as normal income, so you'd have to have a 40% marginal federal income tax rate to end up with $4,000 in IRS debt on $10,000 of forgiven consumer debt, which is an approximation of the maximum marginal rate being 39.6% (which kicks in at $400K income for a single taxpayer.)
I would hazard to guess that people that would be paying anywhere close to a 40% marginal federal tax rate aren't really sweating $10K credit card balances.
Actually, wait, maybe not even that: given that you purchased the debt, you could legally mark it (as the creditor) as having been repaid and then petition (as the debtor) to have your credit score corrected, no? This is what the http://rollingjubilee.org people are doing, at least.