You're entitled to this view, but if you are an entrepreneur running a free service, I'd caution you from believing it.

I run a free service with 50 Million daily end users and if I made such a drastic change, users would (rightfully) be upset.

You seem to be focused on what Disqus has the right to do, while jacquesm is talking about user expectations and the consequences of violating them.

I'm inclined to agree with him that displaying ads on the user's site without explicit opt-in is a major faux pas with the potential to destroy a company's reputation permanently.

I don't think what Disqus did was in good taste, but I do think that it's foolish to expect otherwise from a free SaaS provider.