PHILADELPHIA (CBS) — Kim Holmes, author of the new book, The Closing of the Liberal Mind, accused liberals of attempting to shut down free speech and lamented conservatives not confronting significant cultural changes.

Holmes, during an interview with Chris Stigall on Talk Radio 1210 WPHT, said that if conservatives do not actively engage in the fight over the culture, they will continue to lose.

“The political culture is changing. Conservatives need to understand that it’s happening, not just in politics, it’s happening in our schools, it’s happening in the corporate board rooms, it’s happening in the universities. Obviously, it’s been happening in the entertainment industry for decades. Unless conservatives start pushing back on the political culture and the popular culture, for that matter, they’re going to increasingly and continuously lose these political battles.”

He charged many on the left with trying to shut down the exchange of ideas and implored conservatives to not back down when confronted with protests.

“The push back is to stand your ground and don’t apologize. When it comes down to people shouting you down, you have the angels on your side. You’re standing up for free speech and they’re trying to shut down free speech. That’s a classic liberal value. Frankly, it’s an American value that all of Americans believe in. It’s in the First Amendment. You’ve just got to stand your ground and not apologize. This is actually part of a broader pattern that you’re seeing across the board now. Liberals are turning their backs on the core liberties that they advocated for centuries. It’s not just free speech, but political pluralism, the rule of law and free and open debate.”

Holmes stated that everyone is invested in the right to free speech.

“Whether you’re conservative or liberal, we should be interested in keeping the system open, keeping the Constitutional order open so we can have a free and open debate and not insist that when one side gets in power, everything is settled, history has ended, it’s now the time to use the law to enforce a new code.”