Barbara O'Brien at the Mahablog says:

The fact is that it's the Cheneys and the rest of the Bush campaign who are exploiting Mary Cheney. They're trying to spin Kerry's debate remark the way they spun the Wellstone Memorial. They hope to stir up outrage against Kerry and thereby get back some of the post-debate spin and stop Kerry's climb in the polls....

If Lynne and Dick had just expressed dismay over Kerry's remark once and then let it drop, I'd have called it an honest if unfortunate reaction. Continuing to club Kerry with his debate remark is exploitation on its face. 

Amen.

(She's got a good roundup on the subject, if you're coming to it late.)