I don't think focus is in itself ever a bad thing. But focus of the wrong kind, or managed poorly, can be.

Career diversification ain't a bad thing.

Well, any effort to maximize your potential and ability is a good thing.

The trade deficit is the capital surplus and don't ever think of having a capital surplus as being a bad thing for our country.

Sex is a bad thing because it rumples the clothes.

Being stubborn has helped, being selfish is not a bad thing.