While I'm not sure if the sentences were entirely appropriate for the actions of those people, I think that something like that had to happen. I agree with the judge who said that they'd crossed the line from activists to fanatics. To blinkered fanatics, I'd add.
The thing is that most of the UK population entirely agrees with their cause - something needs to be done. We are seeing the effects of global warming etc. People on this thread throwing about pompous exhortations for action in support of the five are similarly disconnected from reality - people in the UK are already "doing something".
And they're being punished by JSO not doing enough - because this is what their actions amount to. Punishment of the small people. Not the pollutants, not the government, not companies that actually matter.
And because in the eyes of JSO "nothing is being done", it's more than likely that their actions will escalate. This is what the judge's comment means - they've already left behind any peaceful protests. A peaceful protest is sitting outside of the gates of a factory chugging out tons of toxic smoke or gathering hundreds of supporters and organising a march in a city centre - disruptive, yes, but only either affecting those who actually pollute or clearly focused on getting as much attention on the cause as possible IN A PEACEFUL WAY.
Moving on to pure disruption for disruption sake is a big step for an activist organisation. It redefines their core principles and shifts them onto another plane - because JSO have decided that their activities don't work, they need to escalate - whatever they say and however many times they repeat that it was peaceful protesting, it wasn't, was it? What needs to happen before it stops being peaceful? Someone dies? Ekhmmm....
I think that sentencing had to happen - again, I agree it may be too harsh but it's there because of the context, not because it was such a heinous act - it wasn't. But the judge noticed that JSO had clearly started on the route to ecoterrorism. The five's point wasn't to bring their cause to the attention of millions, it was solely to cause disruption, to punish stupid people, with complete disregard to people's wellbeing and life.
If they were let go with a slap on the wrist, their next action would be even more spectacular. And all those laughing at those idiots daring to put their livelihood or hospital visits over the Cause, might change tack if it's their mother denied a lifesaving operation or their child unable to get a heart transplant or just take their exams, or their house gets robbed in a continuing blackout because of a "peaceful protest" disrupting a power plant operation, government networks, or some other lifeline services deemed a worthy target by JSO..