Some actual quotes from the AIBU thread:
*He went into protective mode that's all. He got up to stop her walking any further and you can see her pushing aggressively against him so he stepped up his force to remove her as he probably felt a slight surge of panic and anxiety as to why she wasn't simply turning around and walking away.
It's an insult to Greta Thunberg the way these women behaved last night,
a nobody is getting her 15 minutes of fame
I think it's being somewhat over-analysed!*
And leaving the 'best' till last:
I think he was quite brave actually and acted in the moment to get rid of someone who shouldn't have been there. You can see in the video she pushes back on him so he had to use more force than he had anticipated to remove her