If you recall the story of the woman who was caught in the act of adultery, after the Pharisees tried to test Jesus, Jesus turned to the woman and said "Does no one condemn you?" The woman answers "no" and the lord says "Neither do I. Go and sin no more!" (Jn 8:11). You will find that anytime in the bible, Jesus when he healed or forgave someone of their sins he commanded them "to go and sin no more." So when a catholic goes to confession one of the requirements as stated in the catechism is not to sin again

CCC 1451 Among the penitent's acts contrition occupies first place. Contrition is "sorrow of the soul and detestation for the sin committed, together with the resolution not to sin again."

There a catholic cannot go to confession with the intention of committing that same sin again or with the thinking that if I commit this sin again I can always go to confession next week. One has to have the firm resolution and intention to do everything in their power to avoid the occasion of that sin and to avoid committing that sin. A catholic who approaches the sacrament in such a manner is actually committing a very serious mortal sin called the sin of sacrilege. Therefore confession cannot by its very nature excuse a person from being personally accountable for their actions.

Jesus established the sacrament of penance when he told the apostles in the upper room; “Receive the holy Spirit. Whose sins you forgive are forgiven them, and whose sins you retain are retained." (Jn 20:22-23)

But confession as an act of the penitent has existed right from within the Book of Genesis when God asks Adam and Eve in the Garden of Eden "Why are you hiding?" God has no need to ask us anything. He sees everything. Right from the first sin God calls man to confess his evil doings. Therefore God has established a formula through which we are to be forgiven. This formula is confession. This was laid out by the father in the Old Testament, brought to perfection through the son in the New Testament and continues to be exercised through the Holy Spirit in the present through the ministerial priesthood.

But even with this forgiveness there is still a cost to our sins. Paul makes reference to this when speaking about sacrilegious reception of the body and blood of Christ present in the Eucharist.

Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord.

A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment 14 on himself. That is why many among you are ill and infirm, and a considerable number are dying. (1 Cor 11:27-30)

Paul says this is the reason why some of you are sick and dying. So to think that there is no consequence to sin and that confession is an excuse to sin completely contradicts the teachings of the church which clearly teaches that in order for a sin to be forgiven there must be sincere repentance which includes the authentic desire not to sin again. We can only repent of something that we feel sorry for. And if we feel guilty that we have offended someone, in this case God, then we do try and avoid doing the same thing again.

Also if illness and dying are a result of receiving communion sacrilegiously then one can logically conclude that there is no escaping the consequences of sin even here on earth. To believe otherwise is to put oneself in the position of being an obstinate sinner which Jesus tells us is the unforgivable sin. Unforgivable because we reject the Holy Spirit and the ability of God to forgive us of our sins. This position unfortunately will lead a soul straight to hell upon death. They are lead to hell because they choose to reject God’s mercy and refuse to be in His presence of sanctifying grace. Holding this position is nothing more than self deception if one thinks they will get away with away sins in this life or the next.

All in all a Catholic must go to confession to be forgiven of mortal sins and in order for that confession to be valid they must fully confess all they consciously know they have done with the intent of conversion from those sins through the graces received in the sacraments of confession and then strengthened through the reception of Jesus in the Eucharist.