The marketplace of ideas protects and sustains an intellectual oligopoly
Market regulation is critical for competition within any society. This is also true for the marketplace of ideas. Believing that liberal principles alone can defeat the spread of noxious ideas is wrong. Economic analyses show how a laissez-faire market breeds monopolies that overwhelm market forces and decimate competition. The same is true in this instance. Arguments people feel strongly about are often emotionally charged. They are successful because of how they appeal to base emotional instincts. Not because they are based on hard facts. Left unchecked, oversimplified, hateful, and factually wrong ideas have the opportunity to flourish. One need look no further than the recent growth of right wing populism in the West across the last five years to see how this takes hold. The problem with the marketplace of ideas is therefore in its construction. It assumes all are driven by the pursuit of "truth". History shows us this is a false assumption. And that frequently, the most simplistic and emotionally rousing arguments are those that have the greatest traction amongst the public. And conversely, these often stand apart from reason and logic. History shows us that as troubling ideas grow into something more potent within a society, they give rise to a dangerous elite minority. One that manipulates the wider social environment via emotive ideas built on hateful ideologies. 
The extent of regulation is irrelevant in this context. Disinformation exists regardless of checks and balances in place. Companies, interest groups, individuals, and charities will always lobby for causes they care about. Politicians will always lie. And people will largely choose ideas that they benefit from.