Truth is, by it's very nature, divisive. It separates things. Then again, lies are divisive too. Given that, divisiveness is not the issue but rather what you dividing into?
We can't have no division as the lack of division is problematic because there are no boundaries. Research shows that we don't thrive well without them. Our relationships suffer when they don't exist. We struggle to understand and define where we are or where we are going. Few things are as terrifying as a blank sheet of paper. All possibilities laid out in front of you is pretty harrowing and often we can be paralyzed by having too many choices. I'm a fan of keeping things simple but even that has it's sharp edges. You can make a decision binary when it's not (false dichotomy) and miss the opportunity for a better, combinatorial solution (sometimes called compromise).
If we divide into groups based on our differences, then divisiveness will only lead to more conflict. However, if we divide into groups based on our shared values, then divisiveness can actually lead to positive change. If we divide into groups based on our shared belief in an issue, then we can work together to address this issue. The same thing is true for other issues. If we can all come together and work together, we can make the world a better place.
So, next time you're faced with a divisive issue, don't be afraid to speak your truth. But also be mindful of what you're dividing into. If you divide into groups based on your shared values, then divisiveness can actually be a force for good.