Let it be broke, by a practicing copyright attorney no less:

It's not the law that needs to change, its the economic dynamic. If we, the hip-hop, soul, rnb, jazz, drum and bass, rock, and blues musicians owned the copyright and owned the publishing and owned the masters, we could license whatever we wanted to whoever we wanted for whatever we decided to charge-$5 a sample, whatever. So imagine if Primo owned all rights to "Olympic Runner" (oh sh*t no he didn't)(yes, I did) and you wanted that tight little snare that sounds like a real snare and not some hybrid rimshot (oh sh*t no he didn't)(okay, I'm just f**ing w/ ya, I love your snare sound mighty cool one, it is truly original and dope and is your trademark sound that our grandkids will be able to pick out (like we picked out coltrane vs. adderly or coltrane vs. rollins, don't front)). So when you do a solo joint for BBE or whomever, demand on owning the masters and the publishing, and just license that sh*t to them. Alas, I digress:

The American copyright system is premised upon the idea that CREATORS (artists) and INVENTORS (scientists) should be incentivised to create and rewarded for their word- and that if you reward artists for their creations they will continue to create and society will thereby be benefitted by these creations and it will progress and move forward, and so the incentive the law gives them is a limited monopoly on their creations- a copyright or a patent, depending on what you make. With the copyright comes a number of attached rights- the right to control the distribution and copying of the creation. copyright also gives you full control over the right to make a "derivative work"- a second work that is derived from the original work.

Therefore, to allow any sampling, regardless of how minimal, you are taking away the right to create derivative works that are held exclusively by the copyright holder, because you are letting a stranger take a piece of my creation, and making something out of my creation, without my permission. If we were allowed to do that, then joe-bag-of-donuts could come along and say "ha, I'm going to do the sequel to Do the Right Thing", without Spike's permission, make some wack sh*t, and usurp Spike's business plans; or some idiot could take a couple of characters, say Radio Raheem and Mookie, and make a bullsh*t TV docudrama about Brooklyn, riding on the creativity of Spike, who created these characters and gave them their personalities. See what I'm saying?

P.S.- free sample of the month- "Impeach the President' is in the public domain, which means you can sample it with reckless abandon. I used to have the case citation, but spirit, check on westlaw using "Tuff City" and the name of the song. Let the games begin.

P.P.S.- when you're really good at chopping beats up, you don't have to pay for jack. See DJ Spinna, Psycho Les (beatnuts), some of RZA's and Primo's work, and of course the man from detroit who told you that he'd shoot you if you were looking in his basement window while he was making beats. Now let's go hit some girlie bars.