I doubt that any contributors to Greenpeace understand that they are funding what would be regarded as vandalism by many people. The Western mainstream news media is also highly complicit in the tendency to treat Greenpeace as though their activities relate to a noble cause and are not vandalistic.
Outside the West, there is a much greater tendency to see Greenpeace as simply being a bunch of vandals or hooligans. Two examples in the past few years that spring to mind are the Nazca Lines incident in Peru in 2014, and an attempt by Greenpeace to storm a Russian oil drilling platform in the Arctic region in 2013.
The Nazca Lines incident related to a stunt by Greenpeace at the COP20 climate change conference held in Lima, Peru in 2014, where they damaged a world heritage site in Peru to promote renewable energy. I think this may have been the only stunt ever performed by Greenpeace where they subsequently apologised for carrying it out.
The attempt to storm the oil drilling platform in the Arctic resulted in 30 Greenpeace activists, the "Arctic 30", being locked up in a Siberian prison for about two months under a charge of aggravated hooliganism. JMW raised a good point earlier in the thread that being tough on eco-activists might be counter-productive, as the Western left-liberal media, in conjunction with various celebrities, tried to whip up public feeling that the activists were being disgracefully treated by the evil Russians. The incident probably boosted Greenpeace's funding quite a bit at the time. There was talk of a film being made about the Arctic 30 by the lefty British film director/producer David Puttnam.
There have been previous incidents where statues in London have been defaced as part of some political cause. At the May Day protests in London in 2000, a statue of Winston Churchill was given a 'turf Mohican haircut' and red paint was daubed on the statue's mouth to symbolise dripping blood. The person who defaced the statue, an ex-soldier, was caught and received a 30 day prison term:
It is quite common amongst British lefties to hold figures like Churchill in disdain, but it looks like the UK judiciary is not as sympathetic to the idea of disrespecting Churchill as it is to the environmental cause.