Open source software generally both cooperates and competes. Handled well the benefits of the former offset the costs of the latter and the result is a gain for everyone. --- but software differentiating in consensus rules is the worst kind of competition: competition here can deprive users of the practical freedom to use their preferred software, and the fight risks leaving a salted earth in its wake.

This is not completely unheard of outside of consensus systems: A less powerful version of it exists in the form of file format compatibility. Microsoft was a pioneer of business strategy based on making incompatible extensions to formats, first leveraging their network effect and then-- after introducing incompatible changes-- using it against them, an approach they themselves called embrace, extend, extinguish. Worse than zero sum, these kinds of moves can be tremendously damaging overall.

Bitcoin's creator described alternative implementations as a likely "menace to the network"-- words which I think were spoken with an early insight into the incredible difficulty in making distinct software actually consensus compatible even when that is your highest goal, an art our industry is still just learning.  I wish we'd built mechanisms earlier on for better ways to enable diversity in the non-consensus parts without ending up with unintended diversity in the consensus parts.  But we play the hand we're dealt. The potential harms from consensus disagreements from mistakes in re-implementation are tiny in comparison to those from adversarial implementations which intentionally push incompatible rules.