This is my first time reading any Teenage Mutant Ninja Turtles comics, so I have absolutely no idea what kind of character Splinter will truly turn out to be in this. But here he’s telling his sons that he trained them with the sole purpose of fulfilling his own desire for revenge. Sounds pretty selfish for him to, right from the start, plan to knowingly put them in a life threatening situation because of his personal feelings. I’m not saying he isn’t justified in wanting revenge but making his own burden, theirs as well, is a very self centered thing to do.
On the other hand, this gives Splinter more depth and even makes him more relatable to the reader, because we’re all flawed in some way and so he is.