You cannot prevent anyone from abusing the use of the space available in the blockchain, but given that this space is driven and not free, I do not think that Bitcoin sidechain will be just as cheap as in Ethereum, all enthusiasm for these projects is a waste of time unless the fees are much cheaper than the Ethereum, which may not happen soon .
This reminds me of OMNI layer, which has become most of wallets does not support USDT OMNI layer.
Smart contracts on Bitcoin are a "fun experiment". But they won't be going anywhere, because there are other platforms out there (particularly Ethereum) with an established ecosystem of dApps, tokens, and services. Why "reinvent the wheel", when you can already use an alternative blockchain network for the deployment and execution of decentralized applications? People want to make money these days, so they will choose the platform with the most tokens for speculative purposes (that would be Ethereum). It's this reason why RSK and Stacks aren't very popular these days.
At least, the idea is there. Who knows what the future holds for Bitcoin? Just my thoughts