I hate the term sell-out. The only time I ever use it is to mock people who use the term seriously, or to joke around. However, whether it's true or not, my perception of Metallica is that did, in fact, "sell out". My reasoning? During the early-to-mid 80's, and then the late 80's, Thrash was a popular phase, whether it was commercial or not. Thrash was one of the most predominant forms of Metal, with bands like Slayer, Sepultura, Kreator, Anthrax, Megadeth and the like, hitting it big in the Metal world. Metallica were at the top of this list. Kill 'Em All to ...And Justice For All were Thrash, and Metal in general, masterpieces. The sound was fast, loud, heavy and catchy. James Hetfield sounded mean. The entire work in this period was Metal gold, whether it was big commercially at the time or not.
Then they hit the Black Album, or Untitled, whichever you prefer. The sound was a little different, with more of the softer songs throughout the album, and a slower pace. It was more Heavy Metal than Thrash. This album, however, was still good. I personally enjoyed most of the songs.
At the time of Load, the wave of Seattle sounds had been well-established by bands such as Alice In Chains, Soundgarden, Stone Temple Pilots, Pearl Jam and Nirvana, though the latter wasn't really a Seattle Sound. Suddenly, Rock was back, though more of a modern kind. Load came out in 1996, and it seemed Metallica had ridden the wave of Modern Rock. I'm not[/i] stating that Metallica sounded like any of the aforementioned bands, but as Modern Rock started to become commercialised and bands were riding on a big wave of success from the public demand for this type of music, Metallica had seemingly adhered to this trend.
Now, whether it is true that Metallica decided to cash in on this trend or not, Metallica's sound did change, and for fans of the old, it was not a good change. Load and Reload are not appealing to me, personally, and I find them quite boring. This has nothing to do with the "trend" of disliking commercial, mainstream bands - it is a personal discomfort with the sound from these albums.
I will agree with you guys, however, that it is ridiculous to call bands and artists sell-outs for making it big and hitting the mainstream on MTV, or the like. Kudos to the bands and artists that do make it big, whether I enjoy listening to them or not.