Is it true that the Forcing conflict resolution technique is worse than Withdrawal?
Withdrawal can have negative or positive consequences. On the negative side, left to themselves, people may escalate the conflict to the point that the PM loses control. While time passes, risks may evolve into issues, or issues into problems.
On the other hand, people may calm down and consider each others' needs and opinions. In time, they may voluntarily find ways to meet all needs, or at least reach a compromise. They might also find a new solution. So the problem may solve itself. It's important for the PM to respect the team's ability to solve problems and allow them "space" to do so.
Forcing always has losers and creates the risk of driving a less-than-optimal solution. People don't disagree about issues unless somebody sees an aspect that the others do not see. Odds are, if you force a solution, you've missed an opportunity to find a better solution.
Forcing also implies showing disrespect for the "losers," so it demotivates them. Their decrease in performace can becomes a drag to the team. The negative feelings and the drag, in turn, affects the whole team's performance.
You may not have time to find better solutions. Although forcing ranks as the worst technique, circumstances may force you to use it. If you force a solution, you need to follow up with the "losers" to identify the negative consequences. This shows respect for their needs and their perceptions. It also allows you to find ways to mitigate any shortcomings in the forced solution.