I understand. I accept that you experienced no mixed messages from your conscience.
I suppose I was making an interpretation of your situation. I suppose I was speculating about unconscious or semi-conscious forces in your mind that may have prompted you to act against your conscience, or which allowed you to accept as an excuse something you immediately or later viewed as an inadequate justification.
Just for convenience sake of all in his forum, here is some of what the Catechism of the Catholic Church says about mortal sins:
*1857 For a sin to be mortal, three conditions must together be met: "Mortal sin is sin whose object is grave matter and which is also committed with full knowledge and deliberate consent."131
1858 Grave matter is specified by the Ten Commandments, corresponding to the answer of Jesus to the rich young man: "Do not kill, Do not commit adultery, Do not steal, Do not bear false witness, Do not defraud, Honor your father and your mother."132 The gravity of sins is more or less great: murder is graver than theft. One must also take into account who is wronged: violence against parents is in itself graver than violence against a stranger.*
vatican.va/archive/ccc_css/archive/catechism/p3s1c1a8.htm
I suppose some moral theologians might have some doubts about whether being a party to the suffering of animals in factory farms is “grave matter.” But, I understand your original post, you have no doubt about that. Thus, we are thrown, I think, into the whole domain of “conscience.”
From what I have studied about conscience in Catholic writings, this is an area that, in many ways, is not clearly defined. Among Catholic moral theologians I see lots of debate about many aspects of the issue of personal conscience as it applies to the issue of mortal sin that would merit eternal damnation.
Some Catholic moral theologians hold to the view that simultaneously meeting all three conditions of mortal sin is so hard to accomplish that mortal sin is a rare occurrence.
Other Catholic moral theologians take the view that the three conditions are pretty easy to meet, and so mortal sin is a common occurrence.
Others take a more moderate, intermediate position, or some other completely different approach.
I know of no way to resolve and reconcile these opposing views, except to say that God does not expect ordinary lay persons to be super experts in moral theology, but rather to exercise love of God, agape love for neighbor, and good will at all times as far as possible.
As such, I feel unable to reach any kind of firm conclusions by which to advise you in any definite way.
I do believe that virtually all Catholic priests and bishops you could consult on this matter would advise you that this act in question was not a mortal sin. But, of course, that does not necessarily settle the matter, since mortal sin as related to conscience has a deeply personal and private dimension that cannot be delegated to any other decision maker.
Sorry I can’t help you.
If I were you, I suppose I’d read the New Testament more, and read again all that the Catechism of the Catholic Church has to say about sin and about conscience, and would perhaps read some key documents on the Vatican web site that deal with the issue of conscience.
Also, if you can find a Catholic priest or monk whom you respect and trust, and who will consult with you on this and similar matters, that could be a blessing too. Jesus left us a Church to assist us and guide us. We don’t have to struggle with these matters all alone.
Best wishes.