I'm creating a News Reader app for Tablets and PCs. My app is fetching data from news sources by RSS feed of websites (in the server-side).

But some of these sites are showing some advertising banners at the end of each article.

Should I remove those banners from the feed? Am I legally/ethically allowed to do this?

And what about If I want to put some other ads in my application? (Right at the end of each article)

I mean, If I want to have my own advertising service...

Update: And what if I use feed for content titles and summaries, but use other thing, like Readability API to show full article, and then put my own ads below content? (Readability gets the HTML page, and gives you a clean page without any ads and such.)