Should all ranks within the Signal Corps have the opportunity to re-class to 25D Cyber Defender or only junior ranks?

It can't be open to all ranks because of the COMSEC requirement. COMSEC requires a CAM to be at least a SSG, and an ACAM at least a SGT.

For those of you commenting on the skills required for this: More than half of my graduating class is currently serving in COMSEC Custodian positions, and not doing the least bit of Cyber. My current unit even has two of us, and we're just the CAM and ACAM. This isn't the Cyber MOS a lot of us were lead to believe. If you want to do Cyber, go 17C or 170A Warrant (and 17C IS open to all ranks, based on strengths obviously).

Yes, it should be open to all ranks. If the Soldier has the skills that are required for the MOS, he or she should be allowed to try and qualify for it. He or she will still be serving our country and making a difference in the lives of others around the world.