Yawn!
If the quoted objective of the RMT is so insignificant, then why is it still in the RMT's rule book?
None of the members I know think it’s remotely significant, and it has nothing to do with their reasons for membership, which is about workplace protection, Ts and Cs etc. The membership will reflect the full gamut of political opinions.
The only people I’ve ever encountered who think that clause is significant are posters on here who are looking for reasons to criticise trade unions.