BT is effective for any file, or files that a number of people have, that are generally too large for a single server to feed to numerous downloaders.
All this talk of what do people download with BT, especially with the undercurrent being "if not for illegal applications, then what", is disingenuous at best, and troll-ish at worst. There are numerous, and often recited legal and useful .torrents.
The bottom line is, it is simply another technology. If you have need of this technology, then use it. If you don't need it, simply don't use it. Use it illegally, and you run the risk of being prosecuted.
IIRC, the "most popular and efficient p2p networks" that you refer to were not much more than .torrent repositories for copyrighted material that shouldn't be downloaded anyway. Otherwise, they could have remained in business simply by removing the .torrents in question. It appears that this equated to roughly all of them, resulting in the out of business part.
Finally, to refer to articles found by your link, all he agreed to do was remove links to copyrighted material from his web site. Hardly a condemnation of BT as a technology and tool.