I view FP basically as a redistribution of wait time. Since you don't have to wait in a super long line for a headliner (if you've got the FP for it), then you have free time to wait in line for 2-3 lesser rides. The result is that those "lesser" rides are going to have longer wait times because people have more free time to wait in those lines.
All of this might seem self-defeating, and to an extent I agree with that. I know that if you're planning a day trip or even a short 2-3 day trip in high-crowd periods, it can seem like the deck is stacked against you. I think the impetus behind FP+ is to get guests to stay longer (preferably in a Disney resort) and thus spend more money. It now seems to me that if you have any hope of doing "everything" Disney has to offer, you have to have 6 or 7 park days. Does this bother me? To an extent. But this is a progression WDW has been moving towards for forever--way before FP was invented. It could be argued that as soon as the second park was opened--Epcot in 1982--that it was clear WDW wanted to be a multi-day or even multi-week destination. That trend continued through the opening of DHS and AK, Blizzard Beach and Typhoon Lagoon, the mini-golf course, the regular golf course, downtown disney, etc etc etc.
People don't like this because--unlike opening a new park--there is a perceived "lack of value" in the FP+ program. That's going to be eternally up for debate. Myself, I like skipping the lines 3-7 times per day. I only do standby for rides before noon or after 7 PM. Otherwise I'm going to use FP or come back another day. This is fine for me because I have to fly from Chicago and thus making a WDW 7-8 day trip makes sense once you calculate in the airfare. But if I was just a daytripper, I'd be ticked off at the new system too.