What is the difference between blockstack and Ethereum?

Sure! This is so.

I don’t agree with the point

Just trying to figure out whether I get it right:

Suppose I want to port a smart contract from Ethereum to Blockstack which can only expressed by a Turing complete language.

Would it suffice to have some off-chain logic that repeatedly calls a Blockstack smart contract until the smart contract replies with “done”?

In terms of computability theory, can Blockstack contracts express a single step of a Turing machine, so the repeated triggering of the contract from off-chain would allow performing the Turing machine computation, while having the outcome of each computation step being secured by the blockchain?

Obviously, this would most likely not be the most efficient way to express the computation using Clarity and Blockstack, but I will look at optimization after assessing the mere implementability of Ethereum-representable smart contracts.

Ethereum is a blockchain, whereas Blockstack is a “layer 2” system (i.e. Blockstack is agnostic to the underlying blockchain, and is designed to run on top of existing ones). If you want to make changes to Ethereum, you’ll need to get buy-in from miners and other parties in order to deploy them.