Single word request for a person who speaks by even considering a potential rebuttal

He spoke preemptively. The Free Dictionary defines preemptive as:

taken as a measure against something possible, anticipated, or feared; preventive; deterrent: a preemptive strike against the enemy.

The example given by The Free Dictionary jibes exactly with the OP's example, if enemy is replaced by opponent.

"preemptively", as given in the previous answer is definitely the most accurate word to use in the given context. However, I listened to the podcast again for the particular word and would like to share it here. It is more of a technical term and I did not find its meaning in any popular directory except Wiktionary

The term is steelman (also spelled steel man)

The definition is slightly different from what is given in the question.

From Wiktionary,

Verb

steelman (third-person singular simple present steelmans, present participle steelmanning, simple past and past participle steelmanned)

To refute a stronger version of an argument than what was actually given; to repair flaws in an argument before refuting it.

I will quote the portion verbatim from the podcast episode where I heard this originally, From minute 113.

…If you want to be maximally persuasive, you know Charles Darwin actually did this very very well what I am about to say, In The origin of species instead of strawmanning , I think Sam Harris used this expression, steelmanning, so in other words he would try to anticipate the objection that people would have and then he would not take sort of weak and flimsy version of their argument, he would build it up and make it compelling as possible before he would counter it.

Other Usages:

2012 July 7, Guy Srinivasan, “Wireheading Steelman”, in lw-seattle,

I don't agree with the argument, because of 4. If I were to steelman it, which I may try but after work or maybe during lunch, I would first try to make it impervious to this assault:

2015 February 11, Daniel Armak, “Re: volunteers for feb 24.”, in LessWrong Tel Aviv,

It is possible that while preparing for the talk I will manage to convince myself that the problem is in fact resolved or dissolved. In that case I will treat you to my best steelmanning of the problem, and its resolution.

2015 June 18, rndn, “Going Deeper into Neural Networks”, in Hacker News,

Perhaps the argument should be steelmanned in that we should generally avoid using algorithms which are so complex that they aren't glass boxes.