Unpopular opinion here.
Hearthstone has a playerbase of 50 million players and pulls in $20 million a month. This is not Kevin back in grade school making homebrewed Pokemon cards on construction paper. If you told Kevin to his face that his cards sucked, yeah, you'd be an asshole. Just be nice and let Kevin have his fun; he's not hurting anyone. But this isn't that. This is an enormous multinational company that goes to great pains to locate and hire the best talent in the industry for the specific purpose of performing like the best talent in the industry, in order to earn the shareholders a metric assload of cash.
Do you know why I roll my eyes when people try to drum up pity for Blizzard? Why I don't hold back when I've got a complaint to voice? I've invested myself in these games, goddamnit, and I have some seriously strong opinions about them: good and bad. Blizz can't sit back and welcome the good while simultaneously telling people to keep the bad to themselves. The bad? You want that bad stuff. That's passion, man—that's a good thing. I mean, how many fucking digital card games exist in the world today (check the app store—something like thousands?), and how many of them have the absolute luxury of an active and passionate playerbase chiming in when something doesn't meet their expectations? If you're an indie dev, you don't have that. You disappoint a player, and they say fuck it and uninstall, and you never get a second chance to win them back. Every time someone makes a rage-filled video, it's them saying, hey dude, I'm not happy with this, and I'm giving you the opportunity to fix it before I give up on your game.
You know what you don't want? A bunch of yes-men sitting back congratulating you on how good your game is—right up until they stop playing it.
Edit: blue response buried below
Iksar
I think commentary about 'hey be nice to us' is mostly said jokingly among friends in this circumstance. Toast is a good guy and we have a great relationship with him. I think you'll find everyone here is welcoming to feedback for one of the reasons you mention... passion. We want the game to be better just like the community does and understand that some of the tone that comes along with negative feedback is a result of the passion people have for playing Hearthstone. Part of the fun of being a game designer is the challenges we face when the playerbase evolves and desires different things than when the game launched. I would encourage you and everyone else to keep leaving any feedback you believe we should know about.