Firstly, if an FO said "go around" I would G/A then ask questions later. The chap sitting next to me is fully qualified, therefore I would like to think he called G/A for a good reason.
As for captains being unsafe, and whether to intervene. There are ways to do this, and ways not to.
I flew for just over 8 years before getting my command this year. I never had any captain that didn't listen to me. I always treated them with respect, and posed questions if I wasn't happy. If they couldn't justify what they were doing, then I generally was right. If they could, I was generally wrong (more often the case).
If you still aren't happy, keep going at him. It took me 4 attempts to get a captain to de-ice one time. In that case I had decided that I wouldn't operate if we didn't (obviously it never went that far).