We are meme machines...
Memes == copying with variation and selection (Dr. Susan Blackmore).
For your ideas to spread your immediate network must have: 1) permission to copy, and 2) permission to modify and create variations. Otherwise, your message will never get beyond your immediate social network which we know is something less than 150 people. If you want your reach to be limited just lock your message down with restrictive copyrights.
If on the other hand your mission is to have a far greater impact you're going to need to set your message free:
It's really quite simple. Hold it tight and you limit your ability to have impact. Set it free, and with a lot of luck your message might replicate beyond your echo-chamber. This is why I say over and over and over-- social networking and by extension social media-- starts with getting the permissions right.
Wanting to dive deeper? I highly recommend watching this Susan Blackmore TED talk on Memes and "temes":