So just for climbers not hikers?

Reading the notice carefully, I think it just applies to rock climbing routes only and not the trail.

It states: "the following areas are closed to visitors use..." and then it goes on only to list climbing routes between "South Face" and "Glow with the Flow".
.

That type of closure is fairly standard and probably not controversial. There are a number of areas in the Valley which are closed to climbing right now:

http://www.supertopo.com/climbers-forum/1799122/Yosemite-Seasonal-Closures

To protect Peregrine Falcons, the following areas are closed to climbing:

Arch Rock-All routes from Anticipation to Grokin and on the upper tear from Cross Country Crack to Juliette's Flake.

The Rostrum-Super Nova Wall and all routes on the Rostrum are closed.

Middle Cathedral-North Buttress, Direct North Buttress, Ho Chi Minh Trail, and the Kat Walk above these routes are closed. At the base, the first 5 pitches of these routes remain open.

Yosemite Point-All routes between and including Yosemite Point Buttress, Southwest Face, and Min-Ne-Ah. At the base, the first 5 pitches remain open.

Bolt Wall-All routes closed. Fifi Buttres and The Leaning Tower remain open.

Hetch Hetchy-Wapama Cliff is closed. Kolana Rock is reopened.

Half Dome, South Face-All routes from Autobahn to South Face Route.

These closures will remain in effect until August 1, 2012, or until the chicks fledge and disperse from the area. The avian wildlife biologists recommending these closures are sensitive to climber interests. They work hard to ensure the reproductive success of the falcons, while minimizing the disruption to climbing.

Thanks to the climbing community for cooperation in protecting this magnificent bird!

Ben Doyle, National Park Service, Climbing Management Office.