The only way Steam would ban your entire account is if you attempted to register a CD key that had been released on the internet. Or if you called your credit card company and issued a chargeback. Or if you accepted a Steam gift from someone you didn't know, and Valve decided it was "fraudulent." Or if you logged into a Steam account you didn't create. Or if you shared your account with a friend. Or if you violated the 5,000+ word Steam Subscriber Agreement. Or if you violated Online Code of Conduct, which includes uploading images you don't own the copyright to; using material or information via Steam that infringes any copyright, trademark, patent, trade secret, or other proprietary right of any party; and defaming, abusing, harassing, stalking, threatening or otherwise violating the legal rights (such as rights of privacy and publicity) of others.
That's the only way Valve would ban your whole account.
By the way, the Online Code doesn't specify it has to happen via Steam games or forums--just that as a Steam subscriber, you agree not to do any of it. So according to Valve, if someone harasses, defames or threatens you here on RPGCodex, you can get their Steam account banned.