As I understand, bitcoin basically represents a situation where nodes are expected to (and do) serve other nodes in the network, information that represents the money of all transactions in that network. That is, that regardless of whether nodes(full/light non spv nodes) initiate the connection, recent blocks/transactions/etc are sent by those nodes to other nodes on the network, and that they have unequivocally no choice but to actively participate in the relaying of that information(regardless of content/intent/purpose/etc) to those other nodes. Is there really no way to make a light node(pruned) consistently passive, that is, not send any information relating to the data(possibly also headers) in each block to nodes that request it?(other than some relay bit that seems to be for spv specifically?)
You can start your Bitcoin Core with the
-blocksonly configuration option. This stops your node from requesting and relaying unconfirmed transactions, and disallows inbound connections. Your node will then only request new blocks and the transactions that were confirmed in them. Since your node only forms outbound connections in that case, it will never be in a position to help other nodes with the initial block download. Since your peers would likely get compact blocks from their other peers, your node would also be seldom expected to forward a block.
In result, this should reduce your network traffic to the absolute minimum for staying synchronized with the chaintip, but you'll only learn about transactions after confirmation.
A newly created node has no data to relay. In order to help new nodes start up, existing nodes presumably cannot discriminate against nodes that claim to have no data available to relay.
Therefore I suspect you could, if you had the necessary programming skills, create a Bitcoin node that contributed nothing to the health of the Bitcoin network.
If this occurred on a large scale, people with an interest in seeing Bitcoin survive would presumably need to implement countermeasures that strongly discourage this.