Most important reason: It's profoundly disrespectful
Supposing Thomas Jefferson were some ordinary person, this moves beyond the realm of poor taste. It's a gesture of absolute disrespect, and even one of contempt.
As humanity whittles itself, slow as the whittling may be, into what we will one day become, many of the things we once held sacred are -- sometimes for ill but often for good -- shaved away. The sanctity of a burial space, however, is as un-compromised as it has always been. Its vandalism is an act of malice below even animalism, as creatures such as the elephant are known to create and respect resting places for their dead.
Is Thomas Jefferson's life intrinsically and objectively more "important" than yours or mine? Well, I won't hold court on that. I would also like to make it clear that criticisms of Thomas Jefferson's character, however essential to take into consideration any time we take his life and legacy into account, are beyond the scope of this particular article about guacamole.
Please feel free to register your discontent with the man, but if you ask me, reducing his personal effects to guacamole ingredients is less a gesture of protest and more the immature doings of a no-count felon. Which carries us to our next point.
Second-most important reason: It's against the law
I am not your lawyer, nor am I your secretary. I will not do myself the indignity of researching Virginia's grave-robbery laws on your behalf. Nonetheless, I am supremely confident that municipal and/or state courts have been afforded more than enough legislature to send you to prison.
Third-most important reason: Whatever's in there is surely inedible, and perhaps very dangerous to eat
I do not pretend to know the entire contents of Thomas Jefferson's grave, but we're probably dealing with inedibles from top to bottom: bones, coat buttons, books, and Lord knows what else. This isn't a mere issue of nutritional value; eating such items could be highly dangerous. Consider how much of it might be traced with lead!
Fourth-most important reason: It would taste disgusting
You have finally shocked me. It does not surprise me that there are individuals who would do something as heartless and foul as to rob Thomas Jefferson's grave site -- if there is one lesson taught by our shared existence, it is that the human is a broken animal.
But while I do understand what absence of ethics allowed you here, I do not at all understand the motive that led you to this point. More than likely, the odor will be unpleasant, the texture will be hostile to your tongue, and it will taste like dirt. Why you would expect anything different is entirely a mystery to me.
Fifth-most important reason: It isn't a sustainable practice, because there is a finite amount of stuff in Thomas Jefferson's grave
Thanks to a number of government initiatives, we're slowly making progress toward sustainable, responsible practices when it comes to our food. But if you think tuna is in short supply, you should see the contents of Thomas Jefferson's grave.
It's probably, what, eight feet long by three feet wide? Sure, there are probably enough remains and personal effects for you to make your guacamole. Oh, but now your friend wants some. So she takes some stuff from the grave. And then she tells her friends. And so on and so forth, until suddenly, the grave site is cleaned out entirely.
You can't just grow a new dead Thomas Jefferson. It's a finite, exhaustible resource.
Sixth-most important reason: Guacamole is not your playground. There are rules.
I also insist upon this when I see people add goat cheese, or bacon, or even mayonnaise -- mayonnaise! -- to their guacamole.
Avocado, salt, pepper, lime juice, cilantro. Maybe some onion. At its essence, guacamole is both simple and elegant. It's perfectly balanced. I don't think there is a food on Earth so delicious that is so difficult to screw up. It's a gift. Some of you are incapable of accepting a gift, and so you defeat and humiliate yourself by trying to turn guacamole into your own stupid-assed funhouse.
If you want goat cheese, mayonnaise, bacon, olives, Thomas Jefferson's petrified gallstones, or sour cream in your guacamole, I say to you that you do not understand guacamole. You lack even the slightest appreciation of grace or subtlety. You are doing the dishes with a hammer. Stop it.
Seventh-most important reason: Acquiring the contents of Thomas Jefferson's grave would be a real pain in the butt
At this point we are forced to suppose that you are entirely determined to make guacamole with the contents of Thomas Jefferson's grave. Fine. I hope you're ready for weeks of planning and hours of hard labor.
Firstly, Jefferson is buried in Monticello, a highly trafficked attraction that is protected by 24-hour security. Secondly ... well, do yourself a favor and run an image search for his grave site. It isn't the marker-and-headstone deal you were hoping for. It's a giant stone slab with a large obelisk on top.
It can be moved, but you will need friends, and your work will not be silent. How one could successfully vandalize Jefferson's grave without paying off the guards is beyond me, and I doubt they're cheap. And now, after hours of back-breaking labor and thousands of dollars spent, you're left with a bowl of guacamole that not only tastes terrible, but is entirely unfaithful to the tradition of guacamole. You are a jackwagon. Enjoy.
Eighth-most important reason: You could break a tooth
There is so much stuff in that coffin that could send you straight to the dentist. If you insist on procuring Presidential effects for your guacamole, at least go with Grant's grave. There's probably way less stuff in there to break your teeth on, because he died poor as shit.