I want to go after the special endemic bird in prime morning hours instead of dawdling along roadsides with flocks of common species, and I don't understand the birdwatchers whose every life bird is equally pleasant. I don't have a lot in common with those who just want to tick off birds on their checklist, and learn nothing about them or their identification. There are a lot of these folks on tours. I am uncomfortable with leaders who are patronizing. I have maniac friends who readily do all those things to see birds.
Safety is also always a concern.
Tours seem to offer more safety, but I know of instances when birders have been assaulted on tours to New Guinea and bitten by poisonous snakes on tour in Peru. A friend of mine was killed by a tiger while leading a tour to India. There are also the horrible examples of tourist killings by rebels in natural areas of Uganda while on tours. Birders I know have been robbed and beaten in Costa Rica, shot in the Florida everglades, or suffered burglaries in their motel rooms in Australia. I do not consider world birding to be particularly risky if one takes some common sense precautions, but it is wise to know the politics of an area you plan to visit.