Why would southern staes find it so important to keep a balance between free states and slave states

For the fought for what they belived they also gad high tesion and with high taxes they needed them to make a liveing

If there were more free states than slave states, then there would be a push for a factory-style economy. The South didn't want this, as their economy was heavily dependent on slave labor. Basically, they wanted a balance between free and slave states so as to preserve their economy.