I really don't see what we are arguing about here. There are two aspects to this debate which are actually quite compatible with each other:
1. Genuine cost sharing, regardless of the medium by which it it arranged, is perfectly acceptable and legal (in CAA and EASA land)
2. Running a phoney unauthorised charter operation is illegal (and, IMHO, stupid!), also regardless of the medium by which it it arranged
In addition, anyone facilitating an illegal charter operation is also committing an offence and is liable to prosecution. Thus, it is actually also in the interests of the ride sharing sites not to allow ads which contravene the law whilst allowing ads that do not.
If anyone knows of a specific case in which the law is being broken, I'd encourage them to report it to the authorities.
Simples!