All good things have their limits and the situation is no different when it comes to open discussion in the workplace.
You want vigorous discussion of all sides prior to making the decision, but once the decision has been made, then it is not unreasonable to expect strong support for its execution. Some individuals seek to prolong the debate in the name of dissent. Their behavior can divide and demoralize.
Is that unreasonable? Is that intolerant? No. It is practical and yet you can find some leaders who are so reluctant to shut down debate that they permit their teams to turn into an ongoing college bull session. This is collegiality - no pun intended - carried to an extreme.