Not necessarily a bad practice. Most of the graphs I've seen use this technique, do so to make the changes in value visible, not to deceive the viewer.
Doubling is pretty significant, as is the rate of increase prior to, and dropoff after, 1963.
If some sort of catastrophe befalls our current civilization and future archaeologists attempt to C14 date our fossils and artifacts derived from carbon sequestered during this era, their results will be wildly unreliable.
There are many important changes that are hard to see on a 0-based graph.
If you plot human body temperature in Kelvins, the difference between someone with hypothermia and someone with a raging fever are relatively slight (under 2%).
0 is only relevant for linear utility/impact functions The effect of an isotope isn't necessarily linear in its magnitude from 0. The baseline should be something that matters, like maximum safe dose.
If you have a baseline and a scale that indicates an actual effect, then by all means use it. That’s not the case here, nor has it been the case for any other such graph I can remember seeing. Universally, the bottom is chosen as the minimum value in the data being plotted.
Only if you’re trying to show the CMB and galaxies in the same image. Since doing so would be misleading as to the brightness of the CMB, that seems like a feature, not a bug.
No, if you insist on a uniform colormap that includes 0K (or whatever measurement you're showing the CMB with) then there's absolutely no way to make the CMB visible. The average temperature is 2.72548 K with variations on the order of 0.00057 K. Its incredible uniformity is one of its more important features.
