It's surprisingly difficult, in practice, to believe that it's wrong to sin.
We've been discussing torture and what might be called modern lapsism, and though most of the arguments have been over whether this or that act constitutes a sin, occasionally someone will make a comment like this:
...even if it were a serious sin I would still do it if it meant safeguarding my kids' souls...
I think you can abstract that sentiment from any particular scenario and be left with something most Catholic parents would sympathize with and many would subscribe to.
Let me suggest a couple of reasons why a good Christian, when considering a tough but hypothetical decision, will from the comfort of his own living room resolve to commit a sin should he ever find himself required to make that tough decision.
First, a good Christian doesn't like vainglory, and the better the Christian the less he likes it. "Of course I would do the right thing, come what may," are cheap words in the comfort of your own living room. For many of us, they also ring false. I don't do the right thing in the church parking lot, where the cost is ten more seconds of waiting, and now I'm supposed to do the right thing under coersion by the State, where the cost is my family, because the wrong thing is, technically, a sin not much worse (in the circumstances) than cutting someone off in a parking lot? Since when am I trying to be St. Perfect?
And second, it's really really really hard to believe that an act with absolutely horrific consequences can be required, while the contrary act with absolutely wonderful consequences is proscribed. Even if you know it's the case, that doesn't mean you necessarily believe it. Who isn't, to some degree, a "semi-proportionalist"? A proportionalist would argue that, since the outcome of the one act is so much better, the act isn't a sin. A "semi-proportionalist" would argue that, since the outcome is so much better, the act just can't be a sin.