I'm not familiar with the idiom "spitting on the wrong horn." Here's the context of the quote:
But weigh this [the evils of liberty] against the oppression of monarchy, and it becomes nothing. Malo periculosam, libertatem quam quietam servitutem ["I prefer dangerous freedom over peaceful slavery"]. Even this evil is productive of good. It prevents the degeneracy of government, and nourishes a general attention to the public affairs. I hold it that a little rebellion now and then is a good thing, and as necessary in the political world as storms in the physical.
It's a unilateral contract.