Activist Shareholders
Do more to harm consumers and degrade product offerings than any single factor I can think of. I'm always wary when a business entity comes along and proceeds to tell a widget company how to build a better widget through accounting.
I've been part of the senior management team through wo IPO's and I've seen the damage that investors can do to the companies they invest in. Now that I'm on my own I plan never to deal with outside investment again.