1 John 2:9 -- Anyone who claims to be in the light but hates a brother or sister is still in the darkness.
To disrespect someone is to not show them any love at all, and in fact show the opposite. To disagree is to think that someone is wrong. When we disrespect someone we hurt them, but when we disagree with someone we either respect them and leave it at that, or we try and have a rational argument with someone in order to build them up.
1 Corinthians 13:13 -- Now these three remain: faith, hope and love. But the greatest of these is love.