Liking anything lets the owner spam you.
This just sounds like a scare-tactic to me. That's like saying "following anyone lets the owner spam you", or "emailing anyone lets the owner spam you".
I guess the real point here is to only "like" things that you trust. Just as I won't start following shady looking accounts on Twitter or handing out my email address to every website I visit, I won't "like" shady looking websites.