One of the main ideas of the famous TV show, House M.D., was that in order to generate good ideas, you have to challenge yourself or have people to challenge you at every step.
And I think this is the most valuable lesson which that show has to offer and it repeats it in every damn episode, for the duration of 8 seasons! It must be good!
Leaving House aside, challenge, if it's done in a constructive manner, it is very productive, otherwise it's just ‘contra’. Constructive means basically not to take it personal, to be open-minded, to accept the fact that you might be wrong and to be thankful when you are proven right, but especially when you are proven to be wrong.
Of course, it's much more simple (and safe for your Ego) to just stay with your thoughts, put them on a gold pedestal and admire their greatness from afar. Who is anyone to challenge them, to make you feel uneasy and why do they want so badly to prove you wrong, to make you feel miserable?
But the thing is, challenge (not ‘contra’) is done because of caring, otherwise no-one would invest energy in it, unless it's just ‘contra’. And defeating ‘contra’ is very easy, just let it be! Its flame will burn very fast, because there is no substance in it, just misguided anger.