For most people, I disagree. It takes a lot of willpower to remain stoic when watching such a reunion. While I'm sure Zoro and Jinbe were smiling like Luffy, all three know they must remain collected in case of any unexpected threats. This is how Zoro was able to block an attack while asleep.
Willpower has nothing to do with stoicism or the fact of not crying
The lack of emotion is a conditionning due ones experience and emotionnal openness. Zoro do not force himself not to cry, he simply do not feel like to cry, it's simply his emotional state and a testimony of his detachment in front of the situation. One could say that such detachment is - in the end - unhealthy, but it's not "forced".
When Zoro start to reatach himself to reality (which usually happens when he is touched very deeply in his own feelings) he cries, and no matter what he will try to do, he will not be able to repress himself.
Luffy does not cry out of happyness, unless there is something really cool. He expresses pure joy. In those cases, Luffy do not even think about the frustration, he is just in the purest of of present. The simple joy. He will cry when touch in a hard way tho, but not out of joy. You could say that Oda plays with what is humanly possible to feel in Luffy's case.
If Zoro blocks attack, it's because he trained himself to react to threat (and therefore Haki) it's not a willpower thing, it's simply a result of his experience.
Also.. do not think that it's a good thing or a feet not to cry in such condition. Crying is a healthy phenomenon that allows yourself to evacuate stress and frustrations. You do not want to be like Zoro and trust me, praising his stoicism is not a good idea. Zoro, while being cool and all, pushes himself under a lot of self created pressure. He is lucky to be in a fantastic world, because in reality, Zoro would be in constant burnout and his behavior would bring him in front of a lot of problematic choices.
Crying is the feet here. It's the sign of emotional freedom and deep empathic behavior.