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An Estate is usually a mistake, even with Baron.
This is because you can't "play" the Estate (or a Duchy, or a Province) so it's a dead card until the game ends. If you won't buy the Estate, you'll see your other, more useful, cards more often.
Think about it this way: Everytime you come across the Estate you bought, another card would have taken its place if you hadn't bought it. An Estate is also just 1 point. More often than not, a game is decided by more than just 1 point, with a 5-3 Province or a 5-3 Duchy split for example. That 1 early point is not worth dragging your deck down.
A Copper is a little better, but still not great. That's because your deck will likely improve quickly even if you just buy Silvers and Golds.
When you start playing, you will want to build your deck up to a certain limit before you focus on green Victory cards. It's difficult to know where exactly you still want to buy Action and Treasure cards and when it's time to go into full blown greening mode, but it takes experience to recognize this.
So if you buy a Copper, again it won't help much (but hurt less than an Estate) but it doesn't do a lot either. In the end, that early Copper will only drag you down, so you're better off not buying anything.
A lot of 5/2 openings just pass on the 2 turn. To make up for it, 5 cards are often the most sought after cards. Think about Witch, Market, Laboratory and the likes, all nice cards!
The fact that you have a "dead" turn is negligible when there's a good 5 card.
If there are no good 5 cards and no good 2 cards, then that's pretty rotten luck and you'll have to take a 4 or 3 card with nothing versus an opponent who might get the same card with a Silver.