I was once an anti-theist, not just an atheist. I had malice in my heart towards the idea of being accountable to someone or something outside of myself. I was not interested in actually presenting any part of the bible in its proper context. I have found very few atheists who are intellectually honest enough to argue against Scripture used in its proper context, rather they want to argue against its abuse and misuse.
Anyone can take a verse, passage, or story out of its immediate context or the context of the biblical narrative and twist it to mean something that it doesn't so that that person stands to gain. That is called a false teacher and is warned about numerous times in Scripture.
Matthew 10 is about discipleship. Jesus is giving his disciples their mission and tells them what he expects of them and if they are going to be true disciples the will suffer loss, nothing can be more important to them than Christ, even their own families, if they do follow Christ they will have enemies in their own families, and if they are not willing to suffer loss (take up their cross and follow after him: verse 38) they are not worthy of him.
Anyone who tries to twist that out of context for their own personal gain whether a cult leader who wants to divide people from family members who love them or an anti-theist/atheist trying to gain the upper hand in a debate, they will have to answer for twisting the Scriptures.