"If God is indeed a good and just god, then he couldn't send me into eternal damnation just because I don't believe in him."
This assumes that you are not currently in a state of eternal damnation. In other words, are you being sent someplace new or simply refusing (through disbelief) to move from where you are already? The Christian idea of the fallen man presupposes that man has in fact already (willfully) left communion with God through sin --forgiveness/reconciliation is the path that God has shown us to return to him. It is difficult to accept a gift or instruction from someone you refuse to believe exists.
"If God is not a good and just god, then I have no assurance that he will keep his end of the bargain even if I do believe in him."
This supposes a definition of good and just that supercedes God -- that is, some "higher law" that exists outside of all creation and above God. In which case God is actually not God in the Christian sense, apart from whom there is nothing. This line of reasoning is therefore meaningless.
"So there is no reason for me to worry about the consequences if I don't believe in him."
This doesn't follow.