Nicol Bolas
Terrarian
1. It's not fun. Getting the reavershark is relatively easy, yes, but you still have to do some exploring to get a decent fishing rode and baits, make your way to the ocean and fish. The power it gives was a bit unbalanced, sure, but it was natural regardless, and took some effort to get it.
How exactly was it "natural"? Can you honestly say that, if they never added the Reaver Shark in 1.2.4, you have expected a 100% pickaxe to be received randomly from fishing?
The thing is, the current Reaver Shark is still a pretty strong, pretty early pickaxe. Yes, you can't skip all pre-Hardmode progression, but you can skip some. Your effort will still be rewarded, just not as much.
If I were to cheat the game by providing myself a new pickaxe, I might as well give me a Light pet too like the Fairy and some other stuff. Unless it's a outfit purely for roleplay purposes to look however you want (specially for things like multiplayer or youtube/stream content), then I'd rather not bother.
Didn't you start this post off talking about "freedom to play however you want"? We can all decide for ourselves which parts of the game we want to experience and which we want to skip. The Reaver Shark nerf doesn't change that.
It's only in calling one way a "cheat" that you promote one solution over another. You're not using a world editor or some mechanism outside of the game.
2. Speedrun purposes.
Speedrunners will adapt. Yes, there will be more randomness, but they'll adapt.
Also... Terraria isn't a good game to speedrun. And I say this as someone who watched the AGDQ run of it.
avoiding "contaminating" your world too much by smashing altars. What to do now?
You can fish them up after starting Hardmode. Yes, this means that the infections will be spreading while you're fishing up a bunch of crates. But those need to be contained anyway.