There are a lot of companies whose bad business practices get ousted but don't reach mainstream press. And consumers are the ones that get the short end of the stick.
Would it be a good idea to start a site with reddit-like voting system that ousts bad business practices? Here are some I've read on HN lately:
This would be my first time starting a content site and wondering if this type of content would appeal to readers.
I think the problem you would face is that everyone has a different opinion on "bad" and much of the things you would comment on would be rumours, like what you have listed above. This could lead to defamation cases and all sorts if you aren't careful.
Personally, I would do the opposite. Build a site that praises great business practices and promotes them. Nobody likes visiting a negative site. Everyone is interested in green businesses and sustainability so why not write a blog or profile businesses that are doing great things in this area.
Also if you are intending to make a profit, this might not be the road to go. As social media allows for these discussions to happen on a scale much, much larger than what you would be able to create. However if you want to learn to code, write content, design a site, or draw an audience then it might be a fun little project to do that with.