Leftists always have some fake cause that they use to rouse the public. When I was growing up, it was the Vietnam War. Before that it was "McCarthyism". As I reached college age, the new big cause was No Nukes.
After Communism lost power, leftists gave up touting Marxism and morphed into today's Liberals. They haven't given up their all-encompassing goal of world domination, but the latest fake cause is Environmentalism. Having succeeded with the DDT ban, they reached skyward with the Montreal Protocol and then put all their energy into the Kyoto Protocol (the global warming treaty).
The global warming issue is perfect for leftist propaganda, because it ties together all the hopes and dreams of leftists as well as ordinary people. After all, who doesn't love nature? We must all save the planet!
However, the leftists slant on all these issues is false. McCarthy wasn't persecuting innocent people - although his grandstanding was heavy-handed and probably self-aggrandizing. There really was a threat to national security from highly-placed spies, as ultimately revealed in the Venona Documents. History books should be revised to mention this.
The Vietnam War was not a case of America protecting its business interests against agrarian reformers but was really a case of defending freedom. When we lost our national resolve and acquiesced to leftist propaganda and pressure, over one million Vietnamese civilians lost their lives: half to internal purges and half trying to escape by ocean. Read Le Gulag Vietnamien (translated into English as The Vietnamese Gulag) for the details.
The No Nukes movement had two leftist goals. Primarily, it was to achieve unilateral disarmament, on the premise that the USSR and the USA were morally equivalent and therefore it was the only way to end the Cold War and the risk of Mutually Assured Destruction. However, it as the Soviets - not the Americans - who wanted world domination by force. "Imperial America" was a myth, while the Soviet Empire was real. Ronald Reagan cut through all the fog with a military buildup and with research into missile defense (see SDI). As a result, the US won the Cold War and the USSR dissolved, freeing the Baltic States and the other SSR's. Also, private property rights and religious freedom came to the former Soviet Union.
The secondary No Nukes goal was to persuade Americans that nuclear power was inherently unsafe. This goal was shattered after the Chernobyl incident, and many people realized that the problem was shoddy Soviet engineering and safety practices, rather than any inherent danger. This erased much (but not all) of the propaganda gains made on the Three Mile Island incident and Jane Fonda's movie, The China Syndrome. Leftists are still blocking the construction of nuclear power plants, even though they are safer and less polluting than coal plants. For more information, consult Petr Beckmann's book The Health Hazards of Not Going Nuclear (1977).
Environmentalism sounds nice, but it is not the same as Conservationism which seeks to preserve nature and natural resources for human use and enjoyment.  It begins with the observation that human beings have messed up nature, which is true as far as it goes. But like its Marxist antecedent it dismisses any possibility of people changing voluntarily. Government must intervene and stop people from using insecticides like DDT, even if the scientific evidence of environmental harm has been exaggerated. False heroines like Rachel Carson posed as whistleblowers while actually providing a one-sided, anti-scientific and alarmist account. The DDT ban was eventually relaxed 21 years ago when the UN quietly announced that it was dropping its opposition - coincidentally (?) after I had managed to use Wikipedia to publicize the deception and promote that scientific research that proved DDT was safe to use in anti-malaria programs.
The Montreal Protocol played on inflamed fears of [skin cancer] from ozone depletion, and despite the lack of any scientific basis got laws passed to ban CFC (used in air conditioning and refrigeration). The leftists didn't care about skin cancer, but were just testing the waters. When they found they could sway lawmakers on this topic, they set their sights on a much bigger target.
The Kyoto Protocol is the global warming treaty signed by over half of the world's major countries, with the notable exception for India, China and the United States. It provides for a ban on emissions of "greenhouse gases" on the trumped-up grounds that such emissions will lead to harmful global warming. Actually, it is variations in the sunspot cycle, a natural factor beyond human control, which are responsible for most of the ups and downs in atmospheric temperature. However, billions of dollars have been spent to publicize the leftist, environmental point of view, and even supposedly neutral Wikipedia has helped. It was recently that a backlash began turning the tide. British courts require schools showing Al Gore's documentary to point out several scientific mistakes in it. And Climategate has revealed how supposedly objective scientists and journal publishers colluded to hide evidence against the anthropogenic global warming theory (AGW).