Everyone's different, and that makes for a great number of different strengths and weaknesses. The biggest problem you run into with opinionated people is that they're frequently more interested in offering their opinion than doing anything about it. On the other hand, that means there's no shortage of constructive criticism when you want it.

In short, opinionated people are just another type of person you have to deal with. If you can't make yourself be as opinionated, that's no big deal. If this is a significant problem for you, perhaps it's best to figure out what skills you have that would complement "opinionation".