I'm going to propose a hypothetical situation here. Let's say that biochemists develop a drug which is intended to influence brain chemistry in such a way that people who take it become kinder, more loving, more generous. Now, of course, this drug wouldn't take away all the other good reasons to be kind and loving and generous. It would just provide another impetus for that behavior.
In initial trials, the drug works wonders. People who take it become paragons of virtue, clearly expressing the kinds of behavior that we wish were common throughout the world. First hypothetical question: Would it be a good idea toenforce the use of this drug? To make it mandatory, perhaps put it in the water supply, ensure that children are given this drug from an early age? Again, recall that we haven't eliminated any other reasons for kindness and generosity.
Now, let's go forward a bit. The drug comes into wide use, and it turns out there's an unexpected side effect. Many people, even most people, get the intended effect. But in some people, this drug turns them into bigots, hate-filled demagogues, rapists, murderers, even mass murderers. And there's no particular way to determine who, when given this drug, will end up wanting to chop peoples' hands off or burn them alive. Of course, not everyone ends up with this effect, but a significant fraction do. Second question: Would you argue that this drug is a force for good in the world, that it is reasonable to continue promoting the use of this drug?