Can an analog wired microphone, like a Shure SM58, be connected directly into a USB port using only passive adapters?
The analog microphone signal must be converted into a digital signal that is USB compatible. A device that does this analog-to-digital conversion is known as an "interface." The Shure X2U and MVi are interface devices which provide this conversion.
There are also inexpensive XLR-to-USB "adapter" cables available, but these are not passive devices like most cables. Inside of this type of cable there is an active analog-to-digital interface activated by the DC power supplied from the computer's USB port.