Captain America’s mindset

On the other side of the barricades, Captain America is completely against the Sokovia Accords. And we understand him too, especially if we take into account his most recent history. The Russo brothers did a perfect job with The Winter Soldier, because they created the premise for the entire Civil War. If it wasn’t for the events of that movie, then Civil War wouldn’t have had a political background (or, if it had one, Steve Rogers’ option would have seemed a little out-of-place and would have fallen behind his more subjective reasons).
Thus, the previous Captain America flick revealed that even the most powerful, secretive, and trustworthy organizations can be undermined by those wishing to do so. In this case, SHIELD may be said to have had the best intentions (though we won’t say that). However, since the road to hell is paved with them, it ended with the exposing of HYDRA within SHIELD.
Basically, the need for safety (which is one of the primordial needs) was used against those who needed it (and this is quite a controversial and contemporary issue). And Captain America saw this – as he later said in Age of Ultron, a war cannot be ended before it begins.
From his point of view, the history seems to repeat itself. If before it was SHIELD, now it is the entire UN promising to maintain the peace and end all the destruction. Who’s to say that HYDRA hasn’t infiltrated here too? Who’s to say that these good intentions won’t lead to something worse than even the previous HYDRA plan?
As said, it is pretty difficult to choose a side during the Civil War.
