Provide an example of any consensus rules that have ever been enforced on the Bitcoin network that were not introduced by the developers working on the core client.
Regardless of the examples that anyone comes up with, the fact is that Bitcoin Core does not define consensus. The choices of the users (merchants, wallet creators, exchanges, miners, mining pools, etc) define the consensus. At the moment the users are choosing to use the rules of Bitcoin Core as the current set of consensus rules. At any time in the future, the users could change their minds and choose some other source of consensus rules (such as some other software).
That's true.
Regardless of that, it's not a good idea to have competing consensus rules on the same network. Consensus on the rules, and consequently on the validity of blocks, is what makes the Bitcoin network stable, and hence provides a fundamental part of it's market value (i.e. the Bitcoin price).
Promoting forking of the network in anything but the most dire circumstances is very reckless, and very anti-social. Why would you want to threaten the value of everyone's BTC over non-issues?
The way to handle technical proposals in a way that is
responsible is to discuss it with the rest of the developers. If that can't be achieved, trying to disenfranchise a minority of Bitcoin users by promoting a contentious hard fork is morally highly questionable: it's far more respectful to everyone simply to release a new coin using the consensus rules rejected by the other Bitcoin developers. I think anyone that's been following the various external fork battles can reasonably conclude that, every unrealised fork and every fork that did happen has been woefully ineffective in it's stated purpose and achieved questionable market share. And some Bitcoin forks were clearly entirely cynical in their genuine motives.
This is not to say that the Core team could not become corrupted or make poor choices of direction in future, nobody's perfect. But this issue should be highlighted in the fullest way possible, and if that's to be so,
it should be made clear that in Bitcoin's history up to now, the free-for-all reality of the consensus rules in Bitcoin has only ever been used in a malign way.