Stealing the map to fix something and make additions makes sense, Blizzard originally intended that people would do that,b ut to take a map, add oneor two things, thensay you made it is false and requires no effort. If someone is new to mapmaking and they make a less than favorable map, they'll still learn if they keep making maps and getting feedback from people. However, they'll be strongly discouraged to continue making maps if people steal their maps.
Technically, Blizzard owns all StarCraft maps. It says so in the EULA. People create the maps but they do not own them. Trying to steal a map purely to take credit is disallowed because credit is purely a mark of who reated the file, not who owns the file. By changing this, you're plagiarising work that belongs to Blizzard.
I understand the map unprotecting arguments for the most part, and I'm not an anti-unprotectiong nazi, but I disagree with unprotecting maps purely to take credit for the work you did not do.