If I want to grab all of your tweets, say, don't I have to be approved for API access, some process that they control in some way, and that they can shut off for the bad actors?
Discussion
An API is of course the "official way".
But it is only a matter on time/energy, you can always do web scraping using an extension o a bot.
A lot of copycat sites and content farm sites today are built up in this way.
As soon as the content is online you cannot prevent it from being copied.