Some states do use their own definitions of terrorism to explain why it’s bad when other people do it but OK when they do it, but that’s definitely not a uniform definition.

the calculated use of violence to create a general climate of fear in a population and thereby to bring about a particular political objective.

- Britannica

The use of violence or the threat of violence, especially against civilians, in the pursuit of political goals.

- American Heritage Dictionary of the English Language

the use of intentional violence and fear to achieve political or ideological aims. The term is used in this regard primarily to refer to intentional violence during peacetime or in the context of war against non-combatants.

- Wiki

(Government, Politics & Diplomacy) systematic use of violence and intimidation to achieve some goal

- Collins English Dictionary

the use of violence and threats to intimidate or coerce, esp. for political purposes… government or resistance to government by means of terror.

- Webster’s

https://www.youtube.com/watch?v=cegalOZqmEo

The impacts of the environmental damage are not necessarily worse than the environmental damage from not sinking superyachts in the long term, if it becomes a common enough threat that rich people no longer feel secure in owning them.

The concern with anything too destructive is with the property and safety of workers on board imo, not the ships themselves.

I’d recommend Andreas Malm’s book How to Blow Up a Pipeline if you want to hear more about the reasoning for this sort of thing.

You cannot do that with other social media.

Facebook likes, Twitter likes, Discord reacts, LinkedIn reacts, etc. are all publicly visible. The only possible slight difference with this is that in some cases people might not be aware, in which case the issue would be that it is less obvious to a casual browser than Facebook’s “AncientMariner and 23 others liked this post” rather than that the likes are visible at all.