A valid conclusion might indeed be to stop them being accessible from the outside, by installing such server boards in a network-topologically secure location such as a landfill.
This isn't a fair assessment of the situation. Networks that aren't entirely trusted and controlled can cause spectacular failures. By knowing this, administrators can use BMCs safely. My Poweredge server even came with a warning sticker that had to be removed before the DRAC port could be used.
In general, tools can have "pointy parts" with which the user could harm themselves so long as the risks and proper uses are documented and explained adequately.