Those black boxes degrade sound?

Those "black" boxes on cables are usually low pass filters, cut off above 20KHz. They probably do not degrade the sound, if you only listen to CD playback, and not analog MC cartridges. But are they needed? I do not think so!

MIT and Transparent cables "boxes" contain passive componentry which linearises transit time, such that all frequencies are theoretically in phase at the load end of the cable. Far from degrading your sound the networks are installed to enhance the listening experience --- eh? No they do not wear out, although they can be damaged via inappropriate usage or application of breakin boxes incorporating excess voltages or a DC component.
These networks are not just there for decorative purposes, and if they were't needed, they wouldn't even be there now would they? (indeed an absurdly speculative statement from the uninformed).

Smeared sound? I haven't heard the older generations, but MIT's newer ones do exactly the opposite. Cleaner, more articulate bass, better coherency top to bottom, better defined images, and a larger soundstage.

For image/soundstage freaks like me, check out MIT's MA series, it's a substantial difference over non-networked cables and even their standard lines.