it's not the executable file that's illegal to distribute, it's the GRP file. this contains the art, music, sounds, levels, etc. The shareware version of the GRP is freely distributable. The major difference between the GRP files is the shareware only contains the first three levels of episode one.
I'd like to see several examples of the "majority" of these mods that make use of these edited map files.
I know of a couple that might use heavily edited versions of maps outside of E1L1-E1L3, but most use the first three levels. If the majority are using them, then I've been missing out.
People are going to do what people are going to do. If PikaCommando or someone learns the editor and removes the slimers, I would suggest keeping it to themselves in order to avoid unwanted attention. (3dr no longer "owns" the duke nukem ip)