Super Legato In Scale Playing

I have recently bought the book 'craft of piano playing' by Alan Fraser. I was wondering if the concept of perfect legato could(or should) be incoperated into scale playing or arppeggios at faster tempo. I am experiencing difficulty in depressing 2 notes simultaneously at faster tempo. Hope I'll get an answer to this. Thank you!

Very important question. My answer is, "it depends." At a certain point, if you can't master holding two notes down at a fast tempo, it means there is still some imperceptible collapse still going on somewhere in your system, and you have to resolve it in order to increase your sense of virtuosity and control. However, at a later point, once you have mastered legato, if you keep flogging it like a dead horse, the very thing that empowered you now becomes an impediment. When the knowledge and sense of legato is truly in your hand, then, and only then, can you be slightly less obsessive about actually joining the keys in order to get a singing sound. Unfortunately, without my seeing you and hearing you I can't really tell you what stage you're at. However, with this explanation I hope you'll be able to figure it out for yourself. Good luck and thanks for the apposite question! AFF