Assume I have a component, it is a flip switch (like so), on the switch it states, 120V at 3A or 240V at 1.5A.
Following this pattern, is it safe to assume the switch is capable of servicing in an environment with 5V at 72A?
Also, when does 5V become unsafe to bare contact?
Absolutely not.
The voltage rating is generally based on safety concerns and insulation properties. The current rating is based on the wire construction (thickness), and heat dissipation properties.
For a switch, even the AC and DC properties might not be the same, as any arcing that occurs in an AC use is quenched 120 times/s, while in a DC situation it is not.
Generally less than 40 V or so is reasonably safe for bare contact with one hand, but you would certainly feel 40 V if you touched it with wet skin (I wouldn't try it) -- you might even feel 9 V.
If you pare this question down into its parts, it includes the following question: a) I have a component rated for 1.5-3.0A. Can I run 72A through it?
The limits on voltage and current for a component need to be seen as separate. To quote one answer to this question: "Exceeding the max current (even at a low voltage) may result in the switch conductors getting hot and melting, and perhaps welding together." Exactly.
