Ask HN: Is it ok to monetize an app built on top of other's content?

I have an idea to build a kind of RSS reader app where user can view news, say Hacker News and other bunch of tech news. I plan to monetize the app on subscription basis because I see there's an added value in this app. But the question will be is it ethical to do so? How should I approach this?

For me, It's like a marketplace problem where you need to find seller and buyer. Sellers don't want to place their products in your website if no visitor, and buyer will not even visit that much when there's no seller to look on.

The same like this, I don't have content to show to future buyers, buyers don't want to use this app. But, using other content providers seems not so ethical.

If you have any advice on how we should approach this, would love to hear it.

*Edit: I don't scrape website. I'll use API/RSS provided, in hope will reduce the risk of the ethical matters.