Edit: this comment changed my mind. In a nutshell, if we can't keep a large instance controlled by "the enemy" from destroying what we've got, then we just have to do better next time.

Yes, I would. Even if they are administered by people that have the best interests everyone at heart, sheer size means that they must be taken into account as the tools and clients evolve over time.

It's not that the system itself should be unable to cope with large instances, it's that the only reason for the system itself to gain that capability is in response to the rise or introduction of large instances. Some of what I've seen discussed is the need to change the development roadmap to accommodate the seemingly unexpected rise and possible introduction of very large instances. In other words, those instances are already controlling the direction taken.