These things consume a pretty huge amount of power, more than a steel mill. If they are haphazardly put on a grid without the generation support then the power company has 2 options, brown out or selective blackouts (or risk tripping the whole grid).
It's not silly that an already stressed grid (I'll remind you that NYC just recently asked its citizens to turn the AC to 78 to avoid a brown out) might be pushed over the edge with a new datacenter.