I won't say you are paranoid because we've learn in the (short) history of the web that if 'something might break - it will' :)
IMHO, we don't have the same problem as in C because our JS run inside a sandbox in the browser. There are many limitation that the browser enforce us (=web developers) and we've made some progress in areas like CORS:
https://mikewest.org/2011/10/content-security-policy-a-primer
It will be interesting to see what are the measurements that browsers will take to make sure this powerful feature won't be abuse.