Each is valuable, but we can create as many domain names as are necessary to supply the entire market. Because we can't do that with arable land, millions of people are starving. The current domain name structure allows for more than enough domains to go around, and the proposed naming structure will have absolutely no impact on that number - therefore there is no technical reason not to allow the addition of a few Top Level Domains. With a saturated market, as we have with domain names, where everyone can have as much as they want, the one with a monopoly on that market is guaranteed to make money. Allowing open competition will change neither the level of service, nor the price.
Competition helps keep the market leaders honest by shining light on their activities.
Anyone entering the market would do so out of a motivation for administering domain names, rather than for large profits - a noble intention. Do not restrict entry into this market. It is very capable of keeping itself level.