Not sure how you're curating your "good"news but maybe you could include a submissions API for content providers to submit or link their good news to your aggregator. And maybe a "this sure ain't good news"button could be used to report incorrect articles.

This way maybe larger publishers could send you their good news articles, rather than you digging around to find them.

Also I wouldn't shy away from advertising. What if you only used a curated set of approved advertisers. Things like local solar installers or ethical farm delivery in your area type of things. Not all advertising is from predatory super large corporations.