The real teaching of weaker vs stronger is surprisingly simple, I think. The weaker person is the one who believes that his spiritual security or progress is affected by the outside world—the things he touches, sees, eats, hears, etc. As long as the world can affect his spiritual life, he is at risk. He must be very careful all the time. The strong person, on the other hand, is the one who knows that he is absolutely secure in the love of God; that nothing earned him his salvation and nothing can take it away or damage it.
When the weaker person accidently drinks alcohol that has been mixed into a punch, he becomes afraid and angry. The same thing happens when he flips a television channel and sees something he believes is wrong. He worries that what he sees will defile him and he suffers. When the strong person experiences these things he can simply move on in freedom and peace. He knows that these things cannot touch him spiritually.
There are still consequences, of course. When either of these people drink too much alcohol and become drunk, for example, they can suffer or inflict physical harm. But, even then, the strong believer knows of God’s continual forgiveness and continues his walk. The weak believer suffers shame and guilt. This is not freedom to sin, as some would accuse, but freedom from sin’s effects in the spiritual realm. In the physical/temporal realm, sin continues to have serious effects.