I think this is how most people use Twitter, especially if they go so far as to install any extensions which block ads, clear CSS, etc. - I use Minimal Twitter

I think this is how most people use Twitter, especially if they go so far as to install any extensions which block ads, clear CSS, etc. - I use Minimal Twitter which has been pretty good. The only time I see posts from people I'm not following is when someone I do follow is responding, quote-tweeting, or retweeting. If you use Twitter as is, there are a lot of things promoted for you but it's not any sort of public feed, it's (theoretically) based on who people you follow follow, who they like tweets from consistently, that sort of thing. No Viagra ads are going to be showing up in that.