Jesus, "If you are not with me, you are against me." That's good enough for me. I once talked with a Catholic Priest who did not believe in the resurection and was amazed that I do. That amazed me!
I'm not an expert on scripture by any means, and there are clearly many others in this forum who are, but I think you've got this the wrong way around. What I read (Mark 9:41) is
"For whoever is not against us is for us",
or (in Luke 9:50)
"for he that is not against us is for us."
There is a enormous world of difference!