Liberal is one of those words with dual meaning in today's usage. Either the complimentary or derisory usage. It's just how attitudes change and language usage modifies to reflect it. In the 60s it was a positive to be called Liberal by your contemporaries, now its more pejorative.

What used to be a compliment becomes ironically an insult. Not unlike how the N word is now used in black parlance, but in reverse. Its an interesting evolutionary study: consider the word gay in the 50s and now. Meaning has been re cycled by the generations. On a similar note swear words escalate - damn and blast was inappropriate before the ladies in the 50s, nowadays said ladies happily use the F and C word in public.

Wonder how we will swear in the 2050s?