The necessary thing to understand about the shutdown is that nobody in power seriously claims that the shutdown is, in and of itself, a good policy. Some politicians are trying desperately to spin it as no big deal, or some sort of government vacation, or a “slimdown,” but nobody actually believes it is tenable to adopt the shutdown as a permanent policy. In other words, everyone loses when the government is shut down. That is a fact which nobody is seriously attempting to contest.
Once we accept that the shutdown is, of itself, bad for everyone, the baseline is laid for understanding why the shutdown is the GOP's fault. The entire point of driving the government to shutdown is to try and force democrats to make concessions they would not otherwise have made. Everyone agrees that a world without a shutdown is better than a world with a shutdown. The GOP just hopes that the democrats care more than they do and are the first to say “chicken.”
Democrats have proposed and passed a bill in the senate that would end the shutdown and do nothing else at all. Republicans have refused to take up that bill and pass it in the house. Another important thing to note is that if the bill were brought to a vote in the house, it would pass easily. A combination of democrats and moderate republicans would give the bill an easy majority in a simple vote.
The way the house works, though, the Speaker, who is elected by the majority party, gets to decide which bills are brought to the floor. A small but vocal section of the republican party is against bringing the bill to a vote, so Speaker Boehner refuses to do his job.
You might be inclined to say that we should blame the small group of republicans that are blocking the bill, and not all the other republicans. That is overly generous. Remember that the other republicans choose to caucus with the tea party wing. They came together to choose Boehner as speaker. They bear a measure of collective responsibility for the actions of their party leadership. They deliberately handed power over to Speaker Boehner. They cannot now claim that they share no responsibility in his actions. The moderates, if they wanted to, could bring pressure on Boehner and end things right now. They choose not to. They are afraid of upsetting their conservative base, and would rather just stay quiet and claim they are powerless to do anything about the shutdown.
The republican party, as a whole, is responsible for the shutdown. An attempt to claim otherwise is disingenuous.
The republican party is free to claim that the shutdown is worth it because their goal is worth it. That is a fine argument. They are free to believe that using a shutdown as a hostage tactic is worth it because the ultimate goal is so noble. That does not absolve them of responsibility for the shutdown. If I shoot someone, I can argue that it was justified, but it does not mean that I am not responsible for the shooting. Even if it was a justified shooting, I am still responsible for the shooting.
It is in this way that republicans are responsible for the shutdown. Whether or not they are justified, this is still their shutdown. If they try and pass it off as not their own, then they are refusing to take responsibility for their actions. If a shutdown is worth having to end Obamacare, then they should stand by that. They shouldn't blame other people for what is the obvious outcome of their own negotiating strategy.