Why would it be to anyone's advantage to march against a private company? It is not the enemy. It is simply a company offering its products in the market. The enemy is the FDA and its tyrannical control over the food supply. The enemy is the local city councils that institute prohibitions against individuals growing gardens or raising chickens on their own property. The enemy is the majority of county sheriffs who allow federal enforcers to kidnap people for not pasteurizing their milk. The enemy—as always—is the state.
Some folks complain about the fact that there is no mandatory labeling for GMOs (food containing genetically modified components), but why should there be mandatory labeling at all? Mankind has produced, traded, and consumed food for millennia without labels or printed nutrition information. Why are we accepting the government-centric worldview in which force is the only way to achieve goals? If you are seriously concerned about the presence of GMOs, contact the relevant companies and ask them to either refrain from using them or label them when they do.
So long as you are free to *not* purchase a product from a company, you really have no right to control how they do business. Your power is your ability to 'vote with your dollars' and refuse to do business with a company you don't trust. Personally, I'm not particularly worried about GMOs and even if they were labeled I would still continue to consume them. I suspect that a majority of Americans probably agree with me on this issue. It really doesn't matter though because vocal minorities are often times able to effect significant change simply by making enough noise.
If you insist on marching, why not make the goal voluntary labeling rather than saying such inflammatory things as "Monsanto has got to go!" Obviously no company is going to consent to its own demise, so by your very premise, you marginalize any effectiveness you might otherwise possess. The goal should never be to destroy a company, but to modify (via persuasion, not force) behavior that is potentially harmful. So long as the goal remains increasing government regulation and control of the free market (which is what any kind of mandatory labeling is) I cannot support or be part of this event.
NOTE: This post was written in response to this event.