In 20 years we´re all going to be fucked anyway so this whole debate is pointless. A blocked motorway is a piss in the ocean of inconveniences that will be brought about by Climate Change.
Whether or not these actions have lost the publics support, the fact is the public is not in support regardless and is well and truly asleep anyway. Alternative methods haven´t worked. It is most likely too late already. This is ultimately an action of desperation. People don´t choose to run into motorways for fun, not even hippies.
The time to act is now, not in 5, 10 or 20 years when the world is well and truly burning and the general public have finally woken up. Whether this protest brings meanginful action any closer is highly doubtful. But lets face it meaningful action was not on its way before this protest, so its not like they have really ruined anything either. Fuck it at least they are trying.