They are halving the coin because it needs to be done. All 420 million coins mined in a year of existence is too fast.
With respect, can you scientifically and mathematically prove 'why it needs to be done'. Use references from the past 2 year's worth of currency data, and especially cross-reference coins which have changed rewards, including the ones which survived and the ones which didn't, and show correlation as to their end result.
Because it doesn't "need" to be done. Whether you're at maturity now, next week, or 5 years from now, there's one constant: no use for the coin.