Even with the start of the Fastnet delayed by a day it still won't avoid the bad weather. Looking at the forecast above for Tuesday (from here) its clear its going to be a bumpy ride for the first couple of days.
The argument is that at least the boats will be close to shore if something goes wrong. But some might say that when something goes wrong you might not want to be too close to a lee shore.
Good luck and safe sailing to all those heading out tomorrow.