As for the comment about everyone in your club being easily able to afford the cost of a 'genuine sail' when required I would like to know where in the UK you live. I am live in Cambridgeshire which is a relatively wealthy area of the country and I can say with a reasonable amount of confidence that 75% of the fleet at my local club could not afford to replace their sail once a year (which is what is generally required) with a genuine part but can with a replica part (and the more important part is they do not feel like they are being ripped off).
Whilst I cannot say who can afford what, often when we "afford" is a choice - spend on one thing and we cannot spend (so much) on something else. I just wonder in practice how many dedicated Laser sailors would give-up for financial reasons were they to be forced to buy the more expensive class legal sails. By the time you add-up other maintenance, insurance, Class Assn. membership, club membership, car running costs to events/club a few times per week, personal gear, etc. for many the sail cost starts to become a lower percentage of your total sailing costs. And to give that up because you have to manage with a less than 100% sail for a bit longer may or may not have a massive impact on participation. I suspect it would have a lower impact than people fear - but have no evidence either way.
What I was thinking about with the Class or somebody doing is where clubs have a Laser Open meeting (regatta), if their policy is to allow knock-offs then for whoever holds the trademarks copyright to tell them they cannot call their open meeting a "Laser". Similarly, where a club's Open Meeting (Regatta) is part of e.g. area championship/travellers series or something to let them know that next time their policy for allowing knock-offs will mean the event will be moved to an alternative club. Might not work and I don't really have other ideas (I'm sure somebody in the builders/class can have much better ideas than me).