You make my point perfectly. Government is exactly like terrorism when you remove the concept of consent. McGlinchy was not a moral cause gone amok and he most certainly was not a petty criminal - he was just an idealist fighting for a cause (republican communism) that the majority would not vote for.
Spooner would have said McGlinchy was entitled to secede and set up his own state. Just like the South. What he left out is that handing people over to the tender mercies of violent idealists is a form of tyranny even more severe than ruling by democratic majority.
I think McGlinchy should have been able to secede, but with a few caveats. Firstly and most obviously, he should only secede with his own property and person (or family, if willing). Secondly, he should only convince thru persuasion, not coercion or violence, solicit followers/disciples. Your "handing people over" to "violent idealists" comment doesn't even come close to either of those blatantly obvious requirements.
And finally, should there be any "political dissidents" or "political refugees" who would want to immigrate, they should be allowed to leave his jurisdiction at their leisure, or at the very least, petition anyone they choose to assist them in extricating themselves and their things from their tyrannical environs, if need be.
If you understood Spooner, you wouldn't be making lame comparisons to your scumbag McGlinchy. McGlinchy was inciting riots and generally oppressing others, not putting down external insurgencies and invasions from abroad (there's nothing enlightening about political communism, republican or otherwise).
I highly doubt, had McGlinchy been able to secede (given the chance), he would have been able to last very long on his own since nobody likes dealing with a violent tyrannical nut-job. At the very least he would have starved himself out, or gone out crusading (plundering) and had his head handed to him.
From what I can tell, "libertarians" and "generally conservative" individuals, don't fight (in the violent sense) for a cause, they educate and persuade as much as possible. At the most, they use self defense since that's what their belief system is. As far as I can tell, McGlinchy did none of those things. Hardly a shining example.