[Michael_Michaelangelo]

Purposeful mutations good. Random mutations bad.

Researchers find clues about how antibodies specialize

From the article:

"The AID-RPA interaction must be regulated to bring about the specificity of the mutation," Chaudhuri says. "If this regulation is impaired for some reason, then the B cell would incur a lot of random mutations and that might lead to tumors."

[Ichneumon]

Purposeful mutations good. Random mutations bad.

...and you've misunderstood/misrepresented *that* article, too.