I'am not sure what "protecting" network means when we run nodes . but what if people stop running nodes what exactly going to happen ?
Bitcoin is free.
Nodes are free.
You can't stop free things easely ...
Bitcoin may be free however running nodes is not, maybe you are using a Free wallet (Bitcoin Core) but you will have to run it for 24/7 to help the Network and that's costs electricity which means money .
Money is always going to be there, bitcoin has not yet tap into all our aspects of life, the governments and their fiat still rule the main parts of real life services, if you want to counter electricity usage using the sun and wind would give you freedom from the electricity corporations.
we are all free to take advantage from the sun and wind we just choose not too, either because of limitations or lack of will to do so.