How far should the government intrude on the free market choice?

The only possible answer to this is “to some extent.”  It is impossible to specify a rule that would tell us exactly how much the government should intervene in all cases.
Essentially everyone but the most committed libertarian would want the government to intervene in the free market in some cases.  If there is no intervention, then businesses could sell heroin and cocaine to children.  They could produce child pornography.  You could argue that even slavery would be legal if the government did not intervene at all in the free market.  Hardly anyone would want that.
On the other hand, essentially everyone would agree that we need to limit the degree to which the government can intervene.  Few of us would want the government to tell us that we could not eat meat, for example, or that we could only buy a certain amount of gas each month.  Few of us would want the government to tell us how big our TVs could be or how many hours per day we would be allowed to watch TV.  Practically everyone would agree that there need to be some limits on government intervention.
Thus, it is clear that we have to have some government intervention, but not too much.  Therein lies the issue.  How much is “too much” in any given case?  Let’s look at the issue of food.  Presumably it is okay for the government to say that our food has to be safe.  But how far can they go in defining what is safe? Most people would say that the government could ban foods that would poison us right away.  But what about foods like sugar that are bad for us in the long term but are not going to harm us very much in the short term?  Could the government actually tell us we can’t have food that it deems unhealthy?  Where do we draw this line?
This problem arises in practically every area you can think of.  We want some government intervention, but we do not want too much.  The issue is that not everyone agrees on what is too much.