Should we fear an AGI if it will be equivalent to a human? It seems to me that the first AGIs ought to be able to perform the same sort and variety of tasks as people, with the most computationally strenuous tasks taking an amount of time compared to how long a person would take. If this is the case, and people have yet to develop basic AGI (meaning it's a difficult task), should we be concerned if AGI is developed? It would seem to me that any fears about a newly developed AGI, in this case, should be the same as fears about a newborn child.
There are basically two worries:

If we create an AGI that is a slightly better AGI-programmer than its creators, it might be able to improve its own source code to become even more intelligent. Which would enable it to improve its source code even more etc. Such a selfimproving seed AI might very quickly become superintelligent. 

The other scenario is that intelligence is such a complicated algorithmic task, that when we finally crack it, there will be a significant hardware overhang. So the "intelligence algorithm" would be human level on 2030 hardware, but we figure it out in 2050. In that case we would immediately have superintelligent AI without ever creating human level AI. This scenario is especially likely because development often requires a lot of test runs to tweak parameters and try out different ideas.