As a Catholic, we believe that certain acts are sinful- like suicide, but a person's culpability for the sin depends on the circumstances.
Denying your faith under torture is one thing- denying your faith for a free cup of coffee is completely different. For something to be damning, a person would have to know the sin is a damnable offense and fully consent to it.
There is no full consent in suicide. People just don't up and decide to kill themselves for the fun of it. They are suffer under physical or mental torture, or are mentally ill.
Sadly, certain branches of Christianity believe that certain things are sin and have no consideration for the person's knowledge or willingness. So anytime a person commits suicide- they go to hell.
I believe God judges us by our guilt, not our actions alone. People can carry out the same actions but for very different reasons. Look at killing someone- it is clearly a sin, but few Christians would argue it is always a damnable offense. They understand that circumstances and motivation determine guilt. Killing someone who is about to kill you is different than killing someone for their wallet. It's the same act, but for very different reasons. If you believe this, then you have to concede that suicide deserves the same treatment.