And Christians are symbolically buried with Christ when they are baptized by immersion according to Scripture (
Rom 6:1-5). That should be an indication in itself that Christian are to be buried, and not cremated.
Water baptism - including Jesus' own baptism by John the Baptist - was practiced long
before Jesus' burial. The Jewish practice (admittedly not immersion) dates back to Leviticus. Physically, immersion in water would be a poor representation of a burial. Water had well-established "purification" symbolism long before Paul wrote Romans, and immersion would certainly be a better representation of cleansing from sin or a new birth. Romans 6:1-5 says what it says and
can certainly be read as suggesting that immersion
represents participation in Jesus' death and burial. But
obviously, Paul was not talking about actual
burial practices. It seems to me as though you are reading the passage as though it said, "Therefore we are buried with him by baptism into death
and must also be physically buried like he was." It is obvious that adding this to the passage is ridiculous - it is completely out of place because it isn't what Paul was talking about at all. I have fulfilled my "Christian burial" requirement (if that's how you want to understand Romans 6:1-5) by being baptized. Ditto for Genesis 3:19 - it obviously isn't talking about burial practices at all. To argue that someone who is embalmed, placed in a coffin and buried "returns to the ground" and "returns to dust," but someone who is cremated doesn't, is trying to make Genesis 3:19 do way more work than the passage was ever intended to do.
This is typical, alas, of hyper-literalism: passages are read woodenly, with little regard for what the author of the passage was actually talking about, and then applied completely out of context to support someone's pet position on a topic like cremation. The error is compounded by the propensity of the hyper-literalist to claim that his understanding of the passage is the only one approved by God and that anyone who thinks otherwise is not only wrong but on thin ice with God. This is often true even when huge branches of Christendom and hordes of esteemed Biblical scholars don't share the hyper-literalist's view. It becomes quite tiresome and is one reason that forums like this have difficulty keeping participants. I always feel as though hyper-literalists need to "get out more" - i.e., to do some reading and study outside of their usual sources to see what a
really wide range of views are held by highly informed believers on key doctrines. On issues a
lot more important than "burial vs. cremation," the Bible and God's kingdom can accommodate believers with staggeringly different views.