George Orwell gave 4 good reasons to write in his book "Why I Write".
1. Sheer egoism. This is probably obvious but he also suggested that writers share this with scientists, artists, politicians, lawyers and others.
2. Aesthetic enthusiasm. This has to do with the beauty of the world.
3. Historical impulse. This is the need to let folks know the facts.
4. Political purpose. This, in part, is "the desire to push the world in a certain direction, to alter people's idea of the kind of society that they should strive after".
I don't see anything, in any of the 4, that couldn't have the idea of being genuine added to it. If the person is motivated by a sincere and genuine desire, rather than one intended to deceive, then these all can be answers to the question, "What Matters". This was previously posted in the What Matters section.