Let's talk about Peasant, why it is my number one candidate for most hated card in Dominion, and why it will be my first official selection for the Banlist once ShuffleIT implements it.
1. Centralizing
We all know you can't often play a Peasant board without buying one. In fact, it's often a cause for celebration when you don't have to! Peasant offers the same song and dance every time, and there's nothing you can do about it but play it the way you always do. Now this is not reason enough to ban a card, as there are plenty of cards that do in fact do this.
2. Incredibly Swingy
Oh, what's that? You bottomdecked your traveller and now you're toast. Oh, what's that? You took a calculated gamble drawing 2 cards dead with a 15 card shuffle and you drew your Traveller. Oh, what's that? You drew Disciple without any actions? Oh, what's that? You drew Teacher on the very bottom of the shuffle, and despite your opponent getting Teacher much later than you, he drew it on his first turn and activated before you. Oh, what's that? You lost to a mediocre player for no reason other than how your shuffles went. My heart races with fear every time I roll Peasant on a board. Will I likely lose for no reason at all other than a random arrangement of cards?
3. Ease of Play
But you might remark, "but you can outplay a bad build! You can outplay a mediocre player." And indeed, you certainly can. But real talk, how hard is it to play Peasant, really? You buy Peasant more than once, mass up a ton of a single kind of card, and then slap on +Card and +Action, and if you at any point falter due to a bad shuffle, you're probably just straight up toast. There's no such thing as a bad Peasant build if you play with common sense (please don't make Treasure Map jokes, you know exactly what I mean). There's only more efficient builds, and less efficient ones.
4. Super Long Turns
All of the previous points are claims you can make about Rebuild, or Money strategies. Here's one you can't make: Length of time. Seriously, for all of the annoyances Rebuild and Money games provide, at least they end quick. You're waiting for a century when your opponent calls his teacher, places his token on a card, and then proceeds to play out his turn, optimizing all of the way (either in ways that are actually optimization or ways that are not, which only annoys you further) and eeking out extra plays, while he's up by a trillion and you still didn't play your first Teacher yet. Like why continue at that point?
5. False Hope
Always play out the games. Always play to your outs. Don't give up. You might just win. Yeah, that'll never happen. Peasant gives you false hope that you might be able to crawl back. "WOW, he put that token THERE???" And yet it doesn't matter. He's drawing his deck, and you're not. You can optimize all you like, but the man is up 4 Provinces and will never dud again.
6. A Realization
With all of this in mind, you roll a Peasant board and win easily. And then you have a chilling thought. Did you win because you outplayed your opponent, or because your opponent missed a shuffle with his traveller? Boy, that blows. You won a game for no other reason than RNGesus decreed it.
Closing
Is Peasant the worst, most unfair, most unbalanced card in Dominion? No. But when you get whacked by it, you'll scramble for answers. You'll look at everything you did. You'll agonize for weeks on that loss, that one loss that could have been. And as it turns out, you did nothing wrong. You just didn't shuffle right.