
It's neither more ethical nor more practical to be agreeable than it is to be disagreeable. I think realizing that is an important step to managing interpersonal relations of all sorts.
People may fight with you less if you are a doormat, but they may also trust you less if they realize that your agreement is not genuine. They may also find you more boring if you behave more like a mirror to them than an actual full-fledged person. And if they don't, they likely don't care about your needs and wants. These are probably not the type of people you'll benefit from consistently being around, but they are nonetheless the people who will find this trait most appealing.
Alternately, you may get more positive attention if you are particularly abrasive and disagreeable to people you anticipate others will find unsympathetic, but oftentimes even the worst people are disparaged for reasons that have nothing to do with their real crimes. Often the most insulting things to say in society are the least incisive in terms of taking people to task on what they've actually done wrong. And in terms of practicality, unpleasantness towards others can of course be offputting.
These are just a few considerations when thinking about handling conflict, of course. But it's worthwhile to consider that there is no one right approach and that it can be easy to go wrong on both ends of the spectrum.