The reaction of the user is not suprising. No background-daemon should use all 4 cores and be that noticable. Users don't feel good when the computer starts to make thing on his own they don't expect.

Ubuntu had or has the same issue with a deamon used for the graphical package-administrations-guis rebuilding an index (I forgot the name). They tried to help themselves with appropriate nice-settings, defused the issue, but on old machines you still need to move the cronjob to monthly to have a usable system.

You simply can't use the system properly when a background-process uses all ressources. And one normally want do something else than wait for the system. I consider such behaviour a bug.