Running an event at a loss only makes sense if:
a) It’s to boost the brand, drive retention, etc…lots of big corporate events are run this way.
b) You feel you can build a distinct event brand which will drive revenue over time.
If you’re going with b), you have to make the model work so your variable costs don’t rise as fast as the growth of the event itself. If you can’t make money when you’re small, what makes you think you can earn revenue when you’re big and the costs are much greater?
Not an insurmountable problem, but one worth paying attention to.