Not ALL drums should be mono. The reason for that old axiom traces back to vinyl and a VERY serious problem with high-amplitude, low-frequency sounds when they're being cut to a lacquer.
Lower frequency sounds, on vinyl, are problematic since they require quite a bit of physical movement transferred to your stylus for amplification. But when they're being cut, not only do you have that consideration, but it's essential to check to make sure that NOTHING below around 120 Hz (or thereabouts...different lathe engineers have different "secrets" for this) is out of phase. If they're not, at worst you'll just have a bunch of defective pressings. But the worst-case scenario is when some VERY low-end signal (or a sneaky DC offset) gets to the cutter head, causing it to jump out of the groove it's cutting...or worse still, if the signal actually fries the cutter head because it's been sent a signal it's not physically capable of transferring. But this ONLY applies to vinyl; analog tape and digital sources don't involve a need to mono-ize the low end, unless it helps out musically.
Oh, yeah...scrolling, too. This refers to the width of the "field" between adjacent instances of signal. Some lathes do have a way to deal with this, by adding a "check head" to the tape machine that listens to the audio a fraction of a second before the playback head gets it, and that way, the lathe's scroll width can vary with amplitude. But not all lathes can do this, with the potential result being a record that sounds like this...like this...like this...like this...like this...