I understand that Turing Complete means that Ethereum is robust and able to implement any idea that can be codified including best features from other networks.
Aside from blockchain bloat based on the amount of data that may need to eventually stored on Ethereum what are the possible drawbacks?
Is there a danger that Bitcoin could introduce a Turing complete sidechain while it still enjoys greater economies of scale than Ethereum?
Best Answer
Turing completeness is arguably a matter of design choice. The Bitcoin blockchain was designed to target a very specific use-case (crypto-currency) where Turing completeness is unnecessary. In comparison, the Ethereum blockchain was designed from ground-up to serve as a general platform for a range of use-cases, and for this Turing completeness (or quasi-completeness, to be more accuracte) is valuable in order to allow for generality.
There is certainly a price to pay for this generality (though, depending on your perspective, these may be classed as characteristics rather than actual drawbacks):
As outlined here, the Bitcoin blockchain already supports a non Turing complete scripting language. Past behaviour suggests that it is unlikely that the Bitcoin blockchain, and the associated scripting language, would evolve to an Ethereum style capability any time soon. The blockchain capabilities required for such a change are so fundamental that this would be outside the realms of a simple side-chain. At that point you would effectively have a new blockchain that would diverge from the Bitcoin blockchain and therefore not inherit its economies of scale.