"Obviously, in that instance he was speaking symbolically"
Disciples don't just walk away from symbolic speech! However, the point is that you disagree with others who feel sprinkling is sufficient/not sufficient for Baptism. Do you see my point? I agree with your last statement that one willingly refusing to join the Church (by Baptism) calls his eternal salvation into question.
Regards
I believe God will be just in His judgement. If a person was baptised by sprinkling and they in their hearts believed they were following the will of God, then God will judge them on that basis. I think if you really read the Bible, you should conclude that it should be done in the name of Jesus and by immersion.