/3/ - 3DCG

In Blender, I get awful artifacting when I subdivide a model if I cut an edge loop down the center line of my model and then duplicate > merge vertices (which I've been doing for hard surface modeling off of reference images). It's like the center line edge loop just breaks the subdivision and I get ugly peaking on vertices all along the center line.
Is there any way to avoid this or do I have to work off of a mirror modifier instead of duplicating and joining vertices to stop it?
Also dissolving the center loop fixes the peaking on one side of the model and transfers it all to the other side, try and explain that.