I heard once from R' Yossi Paltiel, and I'm pretty sure he was quoting, though I don't remember who:
We all know the humorous expression "אחרי מות קדושים אמור", After someone dies, we say they were good. But it's not just that we are being kind and sensitive by fudging the truth or focusing on the good and ignoring the opposite, it's that now the neshama is in olam haemes, and in truth every soul is pure and good. Any negativity is from alma d'shikra, which is not a true reflection of the soul.
That's not to say you have to take something not good and say it's good, and I'm not taking a position in this discussion, just providing a perspective I found interesting.
Also, what we say about someone after their passing does have an affect on their soul and its din. This is part of why Chabad minhag is not to give hespedim. We are also concise in our language on the matzeivah.