The big issue with opinion sections is in the era of newspapers, it was obvious you're reading the opinion section. You might get a tease on page 1 to "Read Bill Clinton's views on Bernie Sanders' presidential chances on page 4" but it was clearly in the Opinion section, separated from 'real' news.

In the era of online news, opinion sections are blended with news.

Even The Guardian falls prey to this: go to https://www.theguardian.com/. Click the Opinion tab. Click any of the opinion pieces. The primary navigation reverts to having 'News' highlighted.

Worse, in reader/mobile view modes, the label "Opinion" does not show anywhere.