Why does the first amendment place limits on freedom of speech in the united states?

The First Amendment places limits on free speech because they don't want an abuse of free speech to threaten security. Examples of this would be censoring certain material on the radio, how certain curse words can't be said in different kinds of media, and how hate speech or obscene material are deemed harmful or dangerous. 

I would say that the body of a proposal states a plan of action on how to proceed with a project to bring it to completion and explains the ability of the proposer to tackle the project in such a way as to complete it successfully.