I just want to throw something out there: your thoughts matter and feedback is really important.
I just sent an email to someone close to me trying to persuade them to make a change for the better. I noticed something, I thought a long time about it, and I realized that it actually shows great care to bring hard things up.
But it's not just for big things. When the waiter asks you how your food was, be honest! Don't just say "great!" and grimace as he turns away. The poor restaurant owner will be forced to close his establishment and he'll never know why.
Don't post on social media about how terrible a place is without contacting them first; they're in that business for a reason—they think they can provide something that people want. Give them a chance to make it right. I've found that most places will make it right because they appreciate feedback and want to provide the best products and services they can.
Positive feedback is the most powerful, and that's why I sent my dermatologist a thank you note for his awesome service recently. How often do you think places receive thank you notes? Not often. It'll make their day.
Positive and negative feedback help people improve, and you're actually
doing people a disservice when you're not open and honest with them. There is never a need to be mean or hateful; just be honest.