If you invert the two elements of pcwalton's comment, another way of putting it that might sound less disappointing to your ear would be this: competition is another way of contributing to other projects, if done openly, collaboratively, and in a constructive way.

One of the delightful aspects of this entire HN thread is the interchange between the authors of rg and ag with regard to burntsushi's detailed explanation of the tradeoffs involved, and how the ag author considers making some changes based on learning and philosophy detailed by burntsushi. This interchange is a great bazaar moment in the sense that new ground was staked out. If the proposed moral obligation would be to simply contribute PRs to existing projects (for a slew of philosophical architectural and features differences like Unicode support, etc.), then innovation slows to a crawl because of passivity constraints, bikeshedding, etc.

If you have the talent and capacity to build a better alternative, and share it openly, and explain it so well, as burntsushi has in this domain, then the only moral imperative I see is that you should do so.