You will, if you're a liberal and you live long enough.
I can easily remember when "homosexuality is a mental illness" was the liberal position. Much more recently (1996), Paul Wellstone (one of the most liberal US Senators) voted for the Defense Of Marriage Act. Fourteen years later, no one would expect a liberal Senator to vote against same sex marriage.
When I was growing up, anti-smoking activists were more likely to be religious conservatives than liberals.
I'm slightly too young to remember when there was nothing inconsistent about a Southern liberal politician being a segregationist.
Some left-of-center positions take longer to become conservative. Before, during, and after the English Civil War, John Lilburne disagreed with whatever government was in power. (He also disagreed with his wife, and various other individuals about whom he wrote pamphlets.) He was accused of holding the radical position that all Englishmen above the rank of servant should have the vote. It was a long time till the idea of giving votes to all men and women took hold.
But don't count on any position you now hold taking equally long to become conservative, reactionary, or rightwing loony. In the mid-1980s, same sex marriage seemed as improbable as -- oh, Russia seceding from the Soviet Union.
Do I hear audience members snickering? Marxists, Greens, Libertarians, conservatives, anarchists? I'm laughing back at you. Those of you whose ideologies were based on opposition to or support of the Soviet Union are already worse off than liberals will be. You're irrelevant.
The rest of you might be lucky, and die before your causes become as obsolete as the struggles between Guelphs and Ghibellines.
But if really good life extension comes along, there will come a day when none of those young whippersnappers in college or AARP want to hear about what you think is important. They'll listen to you politely, and go back to discussing whether the Amish should be allowed to keep using their antiquated flying cars.