Potential employers WILL investigate your on-line history. If you behave like an illiterate ass online, chances are you'll also behave like an illiterate ass in real life. Employers don't like that.
However, if the employer finds out that you're an excellent communicator online, regardless of the stated opinion, that ability to communicate effectively becomes a very important asset for the company.
And you thought you had to worry about the government spying on you!