There's two separate forms of consensus in blockchains: 1) consensus about the order in which transactions have occurred and 2) condensus about what rules are valid for the blockchain. But only the first of these forms of consensus needs to be enforced by code. 2nd layer systems rely on the 1st layer to enforce transaction ordering consensus, but they make it simpler and less contentious to fork in the case of disagreement about the rules.

Perhaps you're arguing that there should be more work involved and that the code should try to choose a winner and loser in such discussions by adding extra pressure to the majority side in such disagreements. If so, I disagree with that. I think minority groups should be able to easily select an alternative set of rules if they don't like the rules that the majority is going with. In the end, there's literally little difference though: if a minority doesn't agree with the majority, they can just fork the coin. This happens all the time.

And it doesn't require skilled devs to do so: you can hire super cheap devs who are capable of forking coins. There was actually a program you could download at one point to generate your own "shit coins" based off bitcoin.

I think your tether argument is flawed, because it misses the key detail about tether: Tether is not really a decentralized coin in most senses of the word, because it's value comes from fiat backing, and a central entity, Tether.io, controls that backing. So there's no way to fork tether, unless you're willing to also assume a huge debt to do so.

In case my point in the last paragraph wasn't clear, the problems you mention are problems with centralized backing. They have nothing to do with 1st layer blockchains, 2nd layer applications, or smart contracts. The same centralization problem that prevents forking exists for tether coins stored on 1st layer blockchains such as Ethereum.