While the policy change does fundamentally allow the company to determine what content to keep and to remove I'm not sure how that provides you with a valid concern about opting in your data for the transfer.

IE, if you don't opt in you're basically self censoring yourself as none of the data will get used. If you do opt in, then the majority of it may remain [or be stricken depending on the content you favored bookmarking].

Rather your statement should read "Think twice about opting-out of the delicious-avos transfer. If you opt out then NONE of your data will be kept".