The "There's no benefit from success, only penalties for failure" excuse also holds no weight - Navigation is already such (excepting in TNE). So is Engineering in CT. And also, Admin. They're used for avoiding problems in the CT and later mechanics, seldom for actually accomplishing some PC goals.
I think the difference is that nav, engineering and Admin can be:
A) used creatively in a proactive manner to achieve something (for example, use Admin to game the system and get around bureaucracy, or Engineering to overclock a reactor for a little extra power), while the proposed "loadmaster" skill or task would basically be almost a passive "saving throw" type skill. the other skills have "carrot" uses, this just has a "stick"
B) its hardly "Heroic". I know that Nav or Admin aren't really classical heroic, but we are all aware of situations where a character with good skils in those areas can "save the day" and advance the plot in some useful way (for example, working though the layers of shell corporations and such to work out who
really owns the company the players are investigating), where as loading.....just seems like a boring real job that needs to be done, and I struggle to see a situation where the skill would be anything other than a speed trap.
C) the price of a failure isn't meaningful. Nav, admin, engineering, they all have times when you simply must make that roll, when you really need that jump drive working again, ect. Therefore, their is a meaningful and/or dramatic price of failure. but if you fail a loadie roll, whats the result? either loss of time (if you need to repack the hold), which is a nebulous concept in most games anyway (especially as cargo loading would normally happen in the "downtime" parts of an adventure where there are no time pressures), or a loss of money if cargo is damaged due to improper storage, which, while it something the players care about, is unlikely to actually harm them in the long run (or it shouldn't if your GM is doing his job right.).
Now, I;m not saying that their are no RP opportunities that can come out of cargo and cargo handling. I;m saying that their are no RP opportunities that can come out of the
cargo handling skill, only frustrations and minor, annoying setbacks without any real benefits. I can see that the "job" of loadmaster would be a good crew position for a character without much in the way of starship skills that needs a reason to be on the ship, however (for example, a "gun bunny" ex marine, or that scientist who has no other reason to be roving round the galaxy).
So, in the end, we have a skill that makes it harder for us to do something the players do all the time, but doesn't really let them do something better, new or different.