Easy one this.
ATC have the authority to decide whether you land or not.
400' is about 1.25 nm on a 3 degree glide - not exactly over the numbers.
ATC instruction "OO-XXX make immediate right turn"
PIC response "Tower, OO-XXX going around"
A PIC is responsible for the safety of HIS/HER aircraft, if ATC have got their planning wrong, don't make a drama out of it, but fall back onto a known and safe procedure to take control of your aircraft safety - its a command decision that you are perfectly entitled to make, just as ATC can change a clearance.
ATC can then safely fit you back into the sequence, perhaps by an early turn to downwind.
If you were higher, say 1,000 feet, then an orbit would be perfectly safe - I personally wouldn't wish to play around at 400' - if you got some kind of upset (wake turb or whatever) there isn't much recovery buffer.
At the end of the day, as IO540, Bookworm and others say, commercial airports give priority to the higher paying customers - I for one don't see the problem with that so long as safety is not compromised.