We all know Better Days, the Author Tract it quickly became, and the Marty Stu main character, Fisk. We see him become a secret assassin working for what appears to be a secret society working within the government. He doesn't really even think over why he would want to join them, which is weird since he is still haunted by war flashbacks. As the Alternative Character Interpretation on the Better Days page points out, this might very well be Fisk finally losing his mind. Think about it: everything he has seen, experienced, and been exposed to at this point. The sex he had at age eight, the incest he had with his sister, the fickle women he was with during his life, all the death he saw during the war, all this has led to Fisk becoming an emotionless monster, a creature not wholly a man, no longer human... and the most terrifying part of this? The worst part? Heh. Fisk has a family that Original Life implies he is partially distant from. Irresponsible father? Or a man no longer capable of feeling anything at all?
He likes having kids because he can "warp" them according to a recent Original Life comic.
However, that statement about "warping" them could be considered as a sarcastic remark to unnerve Red, considering the situation in which it was said where he pretty much knew that she was trying to seduce him and he wanted to get her to stop, as he has shown himself fully devoted to Elizebeth and his kids these days, inspite of his job calling him away from them for long periods of time.
People like to criticize the fact that Fisk join the organization as an unsanctioned black ops unit, and have openly referred to the group as a bunch of "American terrorists" at times. However, it seems they're quick to forget that there is no such thing as playing fair in the world of warfare and politics for that matter. Regardless of how some country paints itself as the good guy and seemingly has all their cards on the table for everyone to see, that's not always the case. In fact, it rarely ever is! Anyone who watches Black Lagoon could tell you that. Uncle Sam isn't above playing dirty to get the job done, even if it means contracting an organization like the one Fisk works for "off-the-books."