I'm a node runner.
Based on the configuration settings I set for my node I'm agreeing to store the full block chain of data. I'm also relaying blocks to peers requesting them.
Discussion
If you’ve configured your mempool to accept OP_RETURNs larger than 83 bytes and are relaying them to peers like Libre that normally request them, you’re effectively running a de facto Ethereum node. If you haven’t, then you haven’t opted into what MARA is doing — you’re simply following the consensus rules.