Starfleet was militarized (one of its roles), but not to the extent that Marcus envisioned in the film. They don't operate dedicated warships at the time the movie takes place, rather multi-role ships that aren't made for the one sole mission of killing as best as possible. As written and stated, Vengeance is only there to kill the enemy in war, and all the effort and technology put into it was for that reason, whereas Enterprise could do such (nowhere near as good), but it's not its intent; it was built to explore the galaxy and beyond with a tertiary ability of defending itself and others.
I'm sure Marcus would want the majority of Starfleet's shipbuilding and doctrine to switch over from multi-role vessels and scientific exploration to dedicated warships and fighting skills.
The difference between the two is astounding.