It is indeed most vexing when an uninvited guest appears on one’s doorstep unexpectedly. So why is turning up at a conference without registering considered to be acceptable? When invited to dinner, one is expected to RSVP so that the host knows to expect one, and it is common courtesy to do the same for a conference – by registering early the organizers can plan in advance for catering, for transportation, for room sizes – a whole host of activities where knowing numbers in advance is helpful. If one does not register until the last moment, one cannot complain if rooms for presentations are fully scheduled with no space for additions, or they run out of biscuits at the coffee break. Late registrations are also more expensive, so unless one’s attendance at the meeting was literally a last moment decision, one has just wasted one’s own money purely because one was not organized.
Even worse is the person who “gatecrashes” a conference. Many meetings are organized by professional societies and/ or charities. Yet I have observed with mine own eyes people who exploit the open nature of conferences and attend sessions, parties and other activities without having paid, even to the extent of eating and drinking fare that others have paid for. Such people are the worst of scoundrels and are in effect stealing large amounts of money from said charities. Conferences are expensive to run and someone has to pay for the food that freeloading cad is eating. That is money that could have been spent, for example, on grants for participants who are students or from developing countries, but that now has to be spent paying for the shortfall caused by stowaway delegates.