Your argument is invalid. People who sign up for bitcoin related sites will be warned about proper security protocols as people who are security conscious will not use such sites if they do not tell users who are not security conscious proper security procedures.
Also most/many people who are involved in bitcoin are more computer literate, and these people tend to know to use different passwords between different applications.
OP is completely right. People is stupid, at least most. Accidents happen all the time. Without a centralized place of profesionals whom the mass can blame to in case something goes wrong, there will be a lot of critique about Bitcoin because people don't want to be taken accountable for their mistakes. Only education can fix this but accidents will continue happening.