I understand your concerns, we probably deserve a bit of that considering the franchise history. Perhaps this will ease your concerns. Not counting QA, T1 had about 10 people on it's dev team, T2 had about 15, and TV has 25 right now. Add to that the fact that almost all of the engineering (physics, lighting, shadows, normal mapping, etc...) are required for both SP and MP and you'll see that the engineering staff's task list is 90% core tasks, and only about 10% MP/SP tasks. The real hit comes with the designers and artists, but it's all scheduled out, and our goals for MP are very significant, I think you'll be happy.
So, if that doesn't ease your fears, all I can ask you to do is to wait and see what we do - It's not fair for me to expect you to fall into lock step without seeing the proof, just as it's not fair for you to condemn without first seeing the evidence.