Many people hear the word 'socialism' there and they confuse it with communism or dictatorships. Or they believe socialism is the exact opposite of capitalism. The best way that I think I can convey the idea of what Democratic Socialism is in regard to the Free Market, is with a story.
Two children went trick-or-treating with a large group. The caretaker followed a specific path in a rather opulent neighborhood, and as both children had amazing costumes, their bags were really heavy with their loot.
The first child gets home and their parent, a purveyor of Fox News, decides to examine the candy and test them with a magnet just in case there were razor blades or needles put in them.
Once they are certain that the candy is fine, they let their child eat it all. If the kid gets too sick from eating it all, well, that's a learning experience and they have their baby teeth still.
The second child gets home and their parent, having planned out the route on NextDoor and personally knew the people who were handing out candy, knew that the candy was fine. Instead of inspecting the candy, this parent asks the child to relinquish 80% of their candy.
"If you let me hold onto this for you, I'll make certain you get a piece of candy in your lunch everyday until it runs out." They offer.
The child, while not liking this idea at first, agrees when they count out the candy and realizes there's enough to last until winter break. (Like I said, a LOT of candy)
The next day in school, the two children are at a lunch table together. The second child smiled as they actually had two pieces of candy in their lunch, and a note from their parent saying that the second piece was for their friend.
The first child doesn't even want to look at candy as they got sick last night and threw up from eating too much candy.
The moral of this story is this: unchecked capitalism will seek to maximize profit to a degree that is unsustainable and self-destroying. Democratic socialism seeks to have the people decide how to use a balance of capitalism and socialism for the greater good.
Business interests cannot be left to completely self-regulate, else we'll have the same problem we had in 1929 and 2008 when the market crashed. There is a compelling interest for the government to keep businesses in check when it comes to profit margins; profit is not more sacred than having clean air and water for our children. If you haven't already seen it, I highly recommend the movie "The Big Short". It's a witty and fast-paced film about the housing crisis and uses well-placed humor to point out the failings of our economic system today.