Is it justified to fire a public employee, regarding freedom of speech?

This actually happened quite a while ago (mostly in the months between May and July); I only remembered this by reading another question concerning dismissal.

I probably don’t have all the facts straight, but this is roughly what happened: The cultivation of GMO’s had already been a subject of concern for quite a while, but in May an actual field of genetically modified potatoes was put up in Belgium. Before, the cultivation of GMO’s wasn’t accepted in Belgium, so obviously that field came with a lot of protest.
Not long after they started cultivating that small field, a group of activists (called the Field Liberation Movement) planned to hold a peaceful protest there.
What was planned as a peaceful protest resulted in this. (The actual violence doesn’t start until 3:15)

One of the participants in this protest was a researcher at my university. In response to her actions she was fired, resulting in again, a lot of protest.
The university based its dismissal on the fact that public servants must always be impartial. (Plus, scientific freedom was mentioned to defend the cultivation of GMO’s.)

Normally I’d also be against GMO’s (and I still am), and all for freedom of speech (I reckon that some restrictions of freedom for public servants are quite unjustified and inhumane), but when I watched that video I just couldn’t condone what those activists were doing.

Having an opinion and defending it publicly is one thing, but destroying a field in such a way, trying to convey your opinion by behaving like an animal is in my eyes simply pathetic… That just isn’t a way of having a debate, it’s simply debasing yourself even lower than the ones imposing the cultivation of GMO’s on the people.

To make the question short: What would your reaction be to the behavior of the activists, and for all that matter: what’s your opinion on the limitations on freedom (of speech) of public servants?