From what I can find (most of which is highly polarised / hyperbolic, because of course) it
sounds like they were going to try to use the defence of proportional action (IE that the risk of climate change and the governments inaction on it justifies causing thousands of pounds of damage to an extremely valuable frame, to draw attention to that risk) and the judge may not have accepted that as a valid defence and thus struck it out.
Which the judge is entitled to do if they think the position isn't applicable, or if it isn't valid to the court/relevant etc.
Interesting page on this:
https://hallellis.co.uk/strike-out-applications/
The basic purpose of statements of case (ie particulars of claim or a defence) is straightforward.
They enable the opposing party to know what case is being made against them. They must contain enough detail to enable the other party to prepare to answer it, from a legal perspective.
A successful strike out application against a:
claimant means that they:
have lost all or part of their claim, and
probably must pay the costs of the defendant
defendant means that:
the pleaded defence does not contain a defence known to law, and
subject to further order of the court, judgment is entered for the claimant.
(my highlighting, just to make it bit clearer where I'm going with this)
So if their entire defence was 'but the climate', how is the opposing party supposed to answer that? Is it even worth the courts time? Is it serious or unserious etc.
They were certainly allowed to express their sincerely held beliefs under cross examination, at least, so the idea that they were denied a fair trial and had their human rights breached...eh, I'm a bit dubious on that. Getting bad legal advice isn't a defence either (literally in this case, it would seem)
I think the actual sentencing hearing will be a bit more revealing in terms of whether the above was the case, whether the judge felt they were wasting the courts time, etc and it'll be interesting to see if the claims of 'shit judge' stand up.
If it was a genuine attempt at a defence then I'd not expect them to be long in prison, but I think one of them has been inside before for similar actions and has been quite unapologetic about it so that won't help 'em.