I was once driving in a large city (population, 300,000) and had five people (maybe teens?) on motorcycles (sport bikes) come up to a red light next to me. All five slowed down, and then ran the light. They made a car hit its brakes in order to avoid hitting them. They did "wheelies" and screeched their tires. They were then down the road exceeding the speed limit. My first thought was to pray for them to change their behavior. My second thought, however, was "that's what many people think I'm like when they find out I ride a motorcycle" (even though it's not a sport bike, most do not know the difference!).
This is not really about motorcycles though (as you suspected); it is about our faith. When someone gives a bad representation of the Catholic faith, do you pray that they will change? You should. Then, secondly, do you realize that there are people who think that you are like that? With so many errors floating around regarding the Catholic faith (maybe you used to believe some of them!?), it is important for us to go out of our way to make it is clear what the faith actually is, and also that we are not like those who misrepresent the faith.
It should never be an attack on those who say things that are incorrect about the faith (if we do that, it just looks to the world like internal squabbles), but rather to express that there are errors, and that we are willing to help set the record straight. If we remain silent, then we only contribute to the falsehood. We are accountable for every "careless word" according to our Lord; and that means we are also accountable for every failure of a word that needs to be spoken.
There will be those who intentionally lie about Catholicism, and those who are merely confused and poorly catechized. Whichever it may be, it is our duty to speak the truth in a loving manner so that the world can know that we are not as crazy as those grave misrepresentations that exist out there. Stand fast in the truth; Jesus is on your side.