Whenever people can take an advantage of something, they will.
Lying is effective. More so if it comes accompanied by some truth.
Since the Internet has become the alternative to Mass Media. And mass Media is all about lying to get people to buy your clients products (so they can charge more to their clients), it follows that the Internet would have become a lying cesspool. And indeed, it has.
Heck, even Wikipedia has being found doing information manipulation, eliminating information that is against the believes of whoever is an op there while putting propaganda as the truth.
But this is not only a problem in the Internet. Lying have become the norm in courts. The trick is doing it in a way that the other party cannot prove that you lied. Bonus points if you buy the judge (far too many ways, not all based on money).
And politics. I wonder if one can make a candidate sign a contract in which if he/she does not makes good on his promises, they are automatically, and personally, in debt for 1 million, per each incident. Is far too easy to lie and then do the exact opposite of what you said you would do.