Of course one has to agree with the facts about the disadvantages of extensive multitasking. Cognitive science has rapidly advanced thanks to functional MRI scanning (real-time MRI brain scanning) and PET scans. If results of research say that multitasking

• impairs memory
• causes 4 times greater cognitive processing time
• slows down physical function

then it is difficult to make any sort of argument in favor of multitasking unless the multitasking is of a simple sort whereby you read a book while waiting for an appoint time, check email while waiting for the timer on a batch of cookies in the oven etc. Multitasking of a simple sort may be effective when the nature of the tasks are not conflicting or are not requiring the same kinds cognitive functioning. But multitasking is one area where it is unproductive to argue with science.