One CANNOT be a Christian without the Holy Spirit! When Peter told the people on the day of Pentecost what was required of them, the gift of the Holy Spirit was part of that deal (Acts 2:38). If you deny the Spirit dwells in you, know that you are not a Christian without it. Paul is abundantly clear about this, "You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him" (Romans 8:9 ESV). It does not get anymore cut and dry than that. The Holy Spirit dwells within each Christian. It is by this Spirit that Christians are led (v. 14).
So what is people's problem with the Holy Spirit dwelling in them? I have no idea because it is a comforting thought to me that the Lord left us the ultimate Comforter (John 16:7 KJV). Paul teaches Christians "...your body is a temple of the Holy Spirit within you, whom you have from God..." (1 Corinthians 6:19). Paul is speaking to the individual Christian in this context with references to sexual immorality and sin against one's own body. His point to the Corinthians is to take care of the Spirit's dwelling, our body.
When someone becomes a Christian, they are "sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it..." (Ephesians 1:13-14). Sometimes I think people want to dismiss the idea of the Holy Spirit having any part in our lives because they do not fully understand it. I would dare say, if we waited to except anything until we completely understood it then Christianity would be a dead religion. There are debates about differing ways to interpret various passages because there is not complete understanding. So, just because we might not understand something completely does not mean we should dismiss it all together! "And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption" (Ephesians 4:30). Let us not shun the Holy Spirit, but embrace its indwelling that convicts Christians concerning sin, righteousness, and judgment (John 16:8). I am thankful the Holy Spirit dwells in me.