I don't go to church because I believe that the church kills Christianity and drives people away from the Christian religion. Am I still sinning?
I can’t say that not attending the assembly of the church is a sin, but it certainly is harmful to spirituality. I say this for several reasons.
First, the church is made up of Christians. It is not the building or the assembly for worship. Thus, failing to “go to church” would be like not going home to family. While there are probably some families that members don’t want to go to holiday gatherings of, most families like to be together. Failing to assemble with the family is like saying that you don’t want to be with Christ, because he promised to be where his followers gather. “For where two or three are gathered together in my name, there am I in the midst of them.” (Matthew 18:20)
Not only should we want to be where Christ is, we should want to be where family is. If the assembly of a church is not loving and welcoming, then I can understand that you would not want to be there. But if it is a gathering of Christians, it should be a place where people would want to be. “By this shall all know that ye are my disciples, if ye have love one to another.” (John 13:35)
Failing to assemble with the rest of the church is a sure way to kill your spirituality. The purpose of the assembly is encouragement of one another, as well as worship to God. “And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.” (Hebrews 10:24-25) The writer continues the passage by talking about sinning willfully. I don’t think he is saying that failing to assemble is willful sin, but that failing to assemble will keep us away from that which will prevent us sinning willfully. A battery that never gets recharged is soon dead.
I would like to add one thing about what you said that might shock some people and might surprise you. It is not Christianity that saves, and we should not be worshipping the Christian religion. Sometimes it might be a good thing, on a personal level, for a church to drive people away from the Christian religion, if it drives them to Christ. He is the one who saves, and is deserving of our worship. When we worship the institution and not the person, when we rely on the organization rather than the savior, when we adore the body and not the head, then we have no salvation because we have lost our focus. We should worship Christ, not Christianity.