What about misuse for weapon development? Does the project not massively cut R&D costs (hence lowering the entry hurdle) for potentially malicious actors on the planet?
You can buy the Handbook of Model Rocketry and have essentially all the knowledge that's encoded in OpenRocket or RockSim. You just lack the automated simulations and the parts catalogs (whose weights and dimensions should generally be double-checked anyway). The rockets designed by these programs assume static stability. If you want guidance of some sort, that is entirely on you: that's not remotely a capability available in these programs. If you want to launch at a funny angle, that's also entirely on you. If you want "accuracy" regardless of wind variations, motor variations, etc., that's entirely on you as well. There is a huge distance between the capabilities and the accuracy of simulations of programs like this, and what you would need to come close to developing an effective weapon.
No, actually building the things are most of the work and this program isn't intended for weapons development so you will just save a few tests at most, so it helps marginally.
Anything can be misused by the bad actor. Knives, guns. With AI things are getting easier to develop bio-chemical weapons. There was recently a video of a YouTuber creating a portable rocket launcher in <100 USD.
Maybe we (or somebody in, say Ukraine or Rojava) will need this to defend themselves from the actors having access to missiles right now.