It's to protect you from yourself (and malicious software).
Anyway, where are you trying to move the contents?
I know there's one in /usr somewhere (which you'd need to copy as root), but you could instead move the contents to ~/.themes
PC: LMDE x64 MATE/Cinnamon, Kernel 3.9, Nvidia GT620, i7 3770K, 16GB RAM
Laptop: LMDE x64 MATE, Kernel 3.8.6, i3, 6GB RAM