It's a good question. I think you can & it's identical to this sentence we were given without the definite article. I'm just a learner, but my understanding is that modern Hebrew prefers def art with abstract nouns which embody a general concept whereas English does not. For instance, "Time heals all" in English we do not say "the time heals all" but in Hebrew הזמן מרפא את הכל. Source: Edna Amir Coffin and Shmuel Bolozky, A Reference Grammar of Modern Hebrew (Cambridge, 2005) 132. Referring to a general abstract quality or concept such as הגאווה מסוכנת, "Pride is dangerous" (example from Glinert, Grammar of Modern Hebrew, 21).
My understanding is that האם is optional. Using the copula is unnecessary here because the second part of the sentence is an adjective חשובה. We'd need a native speaker to confirm, but I think if you use האם and a copula it will sound very formal but you would be understood. I don't think omitting the copula here is so much informal as typical. I base this response on my efforts to pay attention to how copulas work in Israeli Hebrew, but I'm just a learner, not a native speaker.