Conflict between main characters in TNG would mean conflict in the chain of command and how well does a ship work with first officer on captains throat?
In DS9 it's understandable, Sisko was working with people who had no starfleet academy background, but argument on the bridge of Enterprise-D, flagship of the federation? That would be ridiculous. If a writer can't write a good story without everybody arguing, that's not a very good writer.
Besides, there is enough friction in everyday life, no need to watch it from TV.