When people talk about “modern art,” they don’t mean (despite what the words suggest) the art being made today; that’s contemporary art. The phrase “modern art” refers to a particular set of styles that flourished during a specific time period, roughly from the early 1900s to the 1960s. It’s a historical term, like impressionism.
Similarly, when you speak of the “civil-rights movement,” people think of the period from around the mid 1940s to the late 1960s, when segregation was dismantled and open racism stopped being respectable, even in the South. That was back when civil rights actually had to do with rights. They are much less likely to associate “civil rights” with today’s proponents of affirmative action and disparate impact (and opponents of school choice and ballot security). This is why same-sex-marriage advocates call their cause “the new civil rights” — they want to make their recently hatched movement sound timeless and unassailable.
And in the same way that Picasso, Kandinsky, and Matisse gave way to lesser talents like Pollock, Rothko, and de Kooning, who in turn have yielded to the excretory art and cow pickling of today, so too have King and Wilkins and the rest been succeeded by the likes of Jesse Jackson, Eric Holder, and Al Sharpton. The insular art world celebrates each new generation as much as or more than the originals, just as the insular Left reveres today’s race activists as if they were actually still fighting for equality. But the public knows the difference between art and the aspiration to be annoying, just as it knows the difference between rights and racial spoils; and in both cases, the language we use reflects the distinction.