That assumes they are economically motivated. As we've seen in recent attacks on other coins, if its a possibility for someone to burn the system down out of spite/malice then the economic incentive doesn't matter.
2. We can go into lower levels and find a number of ISPs specially level 1 ones being able to disrupt the Bitcoin network. Some other single points of failure I can imagine are common routers firmware.
Can Bitcoin never be disrupted? no, does it have mechanisms in place that make it unlikely to be disrupted? yes.