Isn’t it mostly due to suggestion or passion?
Yes, it is frequently due to an overabundance of passion, or, in the case of an addict, and overwhelming urge to engage in an activity that borders on physically debilitating.
I say that as an addict, and I also say that making the final decision to engage in that act makes me liable to damnation.
I certainly
hope that I am not fully culpable for my actions, and that God will tell me as much at my judgment, but it would be idiotic to assume such.
The point is, most people can’t truly know if they met the three criteria for an act such as masturbation to be a mortal sin, so it is better to assume that you did and act accordingly.
What’s more, your what-if scenario here doesn’t really make sense. If someone doesn’t meet the criteria for it to be a mortal sin, then they will be judged according to that reality. If they did, and they did not repent, then they will be damned. We’re not claiming that everyone who has ever masturbated is damned, only that it is grave matter which makes you liable to damnation if certain criteria are met.
If someone commits a mortal sin, they are choosing to cut themselves off form God. If they commit a grave sin, but not in a mortal degree, then they will be judged accordingly.