This is a good and interesting thread - I appreciate the discussion and firm opinions expressed with decorum. Collectively - thank you all for that.
I have a slightly different take on this...
We - as a group of tool-using primates - actually do know what we're doing up there. We understand the environment and the physics governing it. We are well-aware of proven methods to be able to achieve low orbit, geo synch or even translunar orbit. We even know enough about various methods to get to other planets.
What we're doing now is broadening the set of parameters we can work within to achieve the missions, and ultimately, make them profitable. NASA wasn't concerned with profitability or maximizing shareholder value, so they could focus on the engineering principles needed to get the mission done. We already know how to do this.
The envelope is getting pushed because resources are finite, and while Space is hard, there's a lot of ways to skin that cat, and we're trying to figure out the best ways because we have many more options than we used to. It's not that we don't know what we're doing; we absolutely do. We're just balancing the engineering against the needs and against the economics. You're seeing a subtle tug of war between those forces.