That hazard is theoretically there.
However, I feel sure that if I were to fail to disconnect my main breaker before plugging in my genset, I'd briefly be trying to power my entire neighborhood (and more, actually, as currently wired to the grid). Trust me that my generator would pop both breakers in a few tens of milliseconds or less trying to meet the load. I mean, the neighbors have refrigerators, freezers, well pumps, and such just like we do. And if it didn't have breakers, it would stall. And if it didn't stall, it would fry a winding. It seems unlikely in the extreme that a line worker ("lineman" is a specific job title) would be trying to provide a ground path at that exact moment. Possible, certainly. Theoretically.
I'm willing to be corrected if I'm wrong. Please, pipe up if appropriate.
Notwithstanding the above, I fully support connecting generators to houses in accordance with code.