TL;DR - Formats change the economics of Hearthstone to keep it economically and creatively sustainable.
I've been doing a lot of thinking about the recent format announcement, what it really means, and why there are so many differing opinions on it. Here are the conclusions I've reached:
1) Hearthstone's Economic Model = It's Design Model
Blizzard makes money off of HS by selling new cards (and nonsense like portraits). So if they want to keep making money, they need to keep selling cards. But in order to keep people playing, they need to maintain some balance. That's why most of your 2 drops are 2/1, 2/2, 2/3, 3/2 - maybe with an effect. But if all of your 2 drops have roughly the same stats, how do you make new, interesting, balanced cards that aren't just slight variations on existing cards? You can't, so you need to phase out existing cards, which is exactly what Standard does.* They see it as a win-win. They get to keep making exciting new cards for us (to buy) and they keep making money.
If you look at it carefully, this is a business model change as much as a design change. The original model was "buy cards" and the new model is "rent cards". Which leads us to...
2) The Rage
Simply speaking, the rage comes from people who thought they were buying cards (either with time or money). Since there was never before any concept of phasing out cards, a number of people took on a collector mentality and invested in getting certain cards. This "collector" mentality is completely rational if you're buying things and completely irrational if you're renting them, so with this business model change these collectors feel like fools. Their rage is a completely understandable reaction (especially considering that you're not actually buying cards - you're buying a chance to get the cards you want).
But the rage will die down. Collectors who wanted to be competitive will leave; collectors who just love collecting will stay and play in Wild. The rest of the players probably fall into two camps. First, the people who buy every expansion and are effectively subscribers. Second, the f2p players, most of whom will be effectively tourists/chow.
For those who stay, the game will continue to be fun and interesting. But it's important for you to understand that if you pay for expansions, you are not paying for new cards; you are paying a subscription fee. So when one of the new cards is a "2/5 Sledge Belcher Deathrattle: Deal 1 damage to all enemy minions", just enjoy the new flavor and go with it.
I hope someone else finds this analysis useful.
* For those of you who suddenly feel the urge to point out that your cards are still playable in Wild, you are technically correct, but Wild is clearly a second-class citizen. It's the same as telling a pro sports player that they can still play ball, just not in the pro league. The key factor here is the desire to be competitive.