Online college is often more expensive than regular classes. Another disadvantage of online education is complete lack of supervision. If a person is not motivated to finish what they start, then it is probably not a good idea to take an online course.
the major drawback that i could figure out for an online college would be that the fake-ness or the un-authenticity of that very college. one needs to make sure that the college he is looking for is authentic and does exists in the virtual world because if he enrolls himself in any fake college then he might end up jeopardizing his academic career for the rest of his life. this is the major disadvantage other than that it isn't that major as this issue so this is something that should be considered on high priority.