You can, and often should, agree to disagree when another's choices don't negatively affect you or someone or something else you wish to protect. So, you know, in this scenario, that'd work in an "options, not decisions" environment, not the other way around.

On the other hand, as somebody was telling me a while back, "people who care can never agree". Those who are only looking for some personal gain will find some common ground, something for each to gain, and work together towards that, but those who truly care about the issue itself have too much invested in it, be it actual work or resources or reputation or "simple" hope, to feel that they can afford to accept anything but what they concluded is the best option. Hence the trouble.