Major mortgage investors balking at the administration modification plan?

From the WSJ:

Investors who hold billions of dollars of residential mortgage-backed securities are pressing the Obama administration to make changes in its housing rescue plan.
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Some investors say they are contemplating legal action because they think the administration's plan and legislation before Congress would violate their rights. They are particularly concerned about measures that would prevent lawsuits against mortgage servicers, which collect loan payments for the investors and are responsible for modifying loans with homeowners.
"Investors are given rights through the contracts in the securities, and we expect those rights to be honored," said Jeffrey Gundlach, chief investment officer of TCW Group Inc., which manages roughly $52 billion in residential mortgage-backed securities.
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Mr. Grundlach says the program would be more palatable to investors if, for instance, modifications weren't given to borrowers who lied when they took out their initial mortgage.
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Mortgage investors say that rewriting the first mortgage without touching the second violates their rights, because second mortgages are supposed to be repaid second. Modifying the first loan can help the holder of the second mortgage, because it increases the chances the loan will be repaid, they say.
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many loans are serviced by big banks that also hold second mortgages -- and as a result have a financial interest in how these loans are handled.

I keep wondering why any group would ever want to buy a RMBS ever again.