I'm not sure, though, how that undermines the point that Comcast shares in the monopoly of violence with the government. It doesn't make its violence independent of government (at least in the USA): small matters can be dealt with most quickly by those private forces, but in more serious matters, Comcast would call on government violence to provide either a supporting or primary role. The people in conflict with Comcast could do the same, but the difference is that Comcast would actually get the government's help.
Note that this isn't a claim of fascist corporatism or anything: it's part of a healthy society, and really the only way I can imagine a civil society I'd want to live in working. But there's no reason to say that Comcast doesn't have the ability to be co-opted by special interests (its shareholders and affiliated unions, to be explicit about who I'm talking about) and use state-guaranteed violence to impose economic policy in the small on unwilling participants.
I didn't mean to imply that. I was addressing your point of protection of property to be only possible via the state, which I believe to be demonstrably false. The fact that Comcast would likely call the largest and most powerful group of property enforcers (the state) is not particularly interesting.
Does Comcast calmly decide to talk to them about them nonviolently, or does it call in mass State violence to get back control?
You assume a separation between property rights and State power that doesn't exist. They're two sides of the same coin. Capital and property rights don't exist in opposition to the State, but in a mutually-dependent complex of institutions and learned practices.
That doesn't mean you have to throw out one or the other, or both. But it's fair for people to try to change the norms that govern relations between them in a way that generates the social outcomes they prefer.