He might be called upon to resist technically legal authority, whereas Lincoln had it at his back.

To guide and control a headstrong people, smarting under a sense of betrayal, when entering on a movement pregnant with these issues, and at the same time to stand up against a powerful Government on the floor of the House of Commons, was an enterprise upon which any far-seeing man might well hesitate to embark.
Pondering over the invitation conveyed to him in his Chambers in the Temple, Carson may, therefore, well have asked himself what inducement there was for him to accept it.

He was not an Ulsterman.

As a Southerner he was not familiar with the psychology of the northern Irish; the sectarian narrowness popularly attributed to them outside their province was wholly alien to his character; he was as far removed by nature from a fire-eater as it was possible for man to be; he was not fond of unnecessary exertion; he preferred the law to politics, and disliked addressing political assemblies.

In Parliament he represented, not a popular constituency, but the University of Dublin.