In my experience, the truth eventually becomes evident with enough discussion.
Public discourse is not a random walk. It is an evolving phenomenon that gets refined as the participants become more informed about the sources, arguments and facts relating to a subject. It's a messy and seemingly chaotic process, but over time, it works. The force of reason eventually sees through the lies, as long as there are those who persist in showing evidence of the falsehood of the lies.
Lies only work when discussions are superficial, and evidence for the various positions doesn't need to be compared. Substantive discussion exposes lies.
Even when it comes to those who, when shown convincing evidence that their beliefs are based on lies, stay wedded to those beliefs out of emotional/tribalistic attachment, it is valuable to go through the process of discrediting their beliefs, because it demoralizes them, and makes them less effective evangelists for their deluded view of the world.
The process of dialogue and debate is also valuable in its own right. It is beneficial to the population at large for people to make public their reasoning, sources and evidence in the attempt to demonstrate their claims are true.
Again, the benefits of debate are hard to observe on the shorter time scale. It can seem futile at times, especially when you want to immediately enlighten hopelessly deluded individuals, but the forces that guide the evolution of society work on longer time scales, and a determined effort to expose falsehoods and propagate truth through dialogue has benefits on that longer time scale through its long-term ripple effects.