This question already has an answer here:
Why is it illegal to give your opinion/advice about a legal problem or case if you are not licensed or do not have a lawyer/client contract?
Findlaw.com says it's ok if you are just a friend, or if you give general information but not to a specific case.
The reason I am asking is because as I look at it for the first time, it sounds a bit in contradiction with the principle of free speech, or the right to engage in a free non-binding exchange of opinions.
If the main reason is that you may be "dangerously wrong", why isn't the same logic applied to every other aspect of life like cooking, how to fix the foundation of your house.. etc? Putting wrong ingredients in your recipe can poison you. A weak foundation may cause your house to collapse and kill you.