They have good reason to do so--it may be a decision that effectively causes the demise of the USA directly and indirectly.
America poised to lose it leadership role
As far as space exploration and exploitation are concerned, the first century of the new millennia is shaping up to be one of irony. Russia, China, Japan, the EU (through the European Space Agency--ESA), India and even Iran have all announced their intentions to initiate or expand upon manned space missions. Only the United States is pulling back.
Of the six countries that have announced their plans regarding the expansion of their space efforts, four have committed to Lunar missions: Russia, China, Japan and the ESA.
Manned space enthusiasts argue that without a new, greatly expanded presence in space and the Moon, the United States will lose its position as the recognized leader in technology and scientific advancement. They point out that much of today's technology: cellphones, medical instruments, personal computers, and thousands of other technological advancements, were all brought into being because of the initial research done by NASA and its contractors. The technology was created from scratch to fulfill needs recognized by the space agency to fulfill its mission goals.
Therefore when the promoters of space point to the Earthbound applications of space technology, they rightly argue that America will fall behind on every front.
Helium-3 and the future of energy
One of their biggest, loudest arguments, however, concerns the fact that helium-3 has been discovered on the Moon is significant quantities. H-3 is a form of the element that can be used as an efficient material to fuel future fusion reactors.
Fusion power--the underlying nuclear power source of the stars--has been a dream of physicists and nuclear engineers for almost a century. Fusion could provide a cheap, clean, almost inexhaustible energy source to a world with energy needs growing exponentially.
After decades of false starts with toroidal magnetic chambers (Tokamak)  and laser implosion schemes,  H-3 has achieved fusion. The problem is that H-3 is almost non-existent on Earth and manufacturing it is so expensive that operating commercial fusion reactors would be infeasible.
The discovery of H-3 on the Moon changes all that. Lunar H-3 can be mined and shuttled back to Earth using rocket freighters. Suddenly, fusion power as a viable energy source looks very doable.
H-3 would also create a new, multi-trillion dollar industry.
All of this sounds exciting and great, unless you're an American and realize that the countries that would have access and control the market on H-3 would be Russia and China, and to a much lesser degree Japan and the ESA.
Of space, Moon bases and national security
Although the arguments being bandied about as reasons to return to the Moon are valid, the real underlying reason for returning is unspoken, yet urgent: establishing a military presence or preventing our adversaries from establishing one.