RT has had some great coverage of under-publicized issues in the US... issues involving the poor, failing infrastructure, hypocrisy, etc. Yes it's not flattering to the US that these stories are written, but they are true and newsworthy and should absolutely not be suppressed.
During the election, RT ran a unflattering stories about both major candidates. This is now being spun as "trying to sow discord" in the US. Journalism is supposed to shine a light on things that need to be improved, it is supposed to rally people to act to fix those problems.
If you read the major newspapers in the US, particularly in the section on world affairs, there is a steady stream of stories that address the dangers of living abroad, the corrupt politicians, the failing infrastructure, etc. These stories may or may not be true (many are obviously overblown to anyone who has visited those countries) but the purpose they serve is to help foster the idea of American exceptionalism.
Our papers don't have to run headlines like "Americans happiest citizens in the world" or "America has the cleanest water and the happiest children in the world" when it can simply run stories that make other nations (particularly political adversaries) seem far worse.
We still don't know much about the Hillary Clinton or Podesta emails as none of the few possibly troubling things (mostly campaign finance violation stuff) has been investigated. RT ran stories about that topic when it was fresh during the election, even when the major US papers were focused mainly on rude things Trump had said.
When RT first launched I was surprised that it was "allowed" to exist simply because of its origin. But after reading the reporting for several years I came to appreciate that it was offering a view of the US that was not really available from American news outlets. This makes RT valuable to the sharing of ideas and the creation of an informed public.
Twitter's decision to block the advertising is cowardly in so many ways.