Of course all the the RDer's would say "Yes, Yes, Yes" to this suggestion. During those first couple of hours when
I want to ride using the SB line I don't want to compete with anybody in the FP+ line. Then once the crowds build and the standby lines start getting longer, I want the FP+ line to open up so I can bypass those now growing lines.
Look at Touring Plans wait times for yesterday at Space Mountain.
http://touringplans.com/magic-kingdom/attractions/space-mountain/wait-times/date/2014-07-30
or more broadly, Josh's wait time estimates on EasyWDW.
http://www.easywdw.com/cheatsheets/mk_cheatsheet_easyguide2.pdf For MK or
http://www.easywdw.com/cheatsheets/hs_cheatsheet_easyguide2.pdf for DHS
Even with FP+, the shortest wait times of the day are at RD. They may not be the as low as they were under FP- but they are still the lowest of the day with few exceptions. But that's not good enough. The "in the know" RD crowd wants their already shortest SB wait times even shorter.
By not having FP+ in that first hour, the people that would have booked FP+ during that time, even if it's unnecessary, now are booking FP+'s when the lines are longer. Making the SB lines longer the rest of the day.