approach to succeed, given adequate hardware.
The stagnation of AI during the seventies and eighties does not have much
bearing on the likelihood of AI to succeed in the future since we know that
the cause responsible for the stagnation (namely, that the hardware
available to AI researchers was stuck at about 10^6 ops) is no longer
present.
There will be a strong and increasing pressure to improve AI up to
human-level. If there is a way of guaranteeing that superior artificial
intellects will never harm human beings then such intellects will be created.
If there is no way to have such a guarantee then they will probably be
created nevertheless.