So much of politics is perception and public relations. If you truly believe in whatever your political goals are, then you have to try to make them sound pleasant, or desirable to other people in order to achieve those goals. When one's case is unconvincing and undesirable on it's own merits, people often turn to deceptive methods of convincing others, such as propaganda and rhetoric.
How does an 'illegal immigrant' become an 'undocumented worker'? How does 'global warming' become 'climate change'? How does the 'War on Terror' become an 'overseas contingency operation' (seriously?)? Heavy polling.
'Illegal immigrant' or 'alien' has a strong negative connotation, for one example. But we have a negative reaction for good reason; we don't like breaking the law, or those who do it. Conservatives are unafraid of a truthful, but negative, connotation. Since it's in a liberal's best interests for people not to react negatively to this concept, they deceptively employ the use of rhetoric to soften the 'illegal immigrant' and make him an 'undocumented worker'.
When did 'man-made global warming' suddenly up and turn into 'climate change'? Not coincidentally, right in the midst of heavy criticism from many scientists around the world who claimed that the science behind 'man-made global warming' is at best inconclusive, and at worst fraudulent. So, right as the cry 'global warming is a hoax!' starts to roar, the environmental left quickly detatches themselves from global warming and instead turns to 'climate change'. Conveniently, climate can change in any direction, may or may not be due to man's activity, AND doesn't have the negative stigma that's attached to 'global warming'. While it still essentially represents the same front for the same movement, the rhetorical shift allows them to proceed without the baggage. Or at least, they hope that's what it will do.
The most egregious, and comical, of the examples I've chosen to illustrate the left's deceptive use of rhetoric is the Obama administration's failed attempt at renaming the 'War on Terror' the 'overseas contingency operation'. This is a flagrant example of Orwellian newspeak, laughable on it's face. But the intent should be obvious here; the perception that the War on Terror is real is politically treacherous for the left. They hope renaming it to some vague, amorphous operation will take focus off of it at home, and perhaps soften views of America abroad. Both of those goals being stupid and dangerous.
Since Conservatives are unafraid of the truth, even when the truth is difficult, you won't find us resorting to such blatant rhetorical shifts in order to make our case, or to distance ourself from something that has become politically unpopular. If we want to convince someone of our position we need only articulate it to them in a straightforward, no-nonsense manner. And if that doesn't work then we just chalk that up to what Masta Killa called "some savage people that are lost beyond reach."