Make I please ask what you mean when you use the words 'fabricated family trees' ....
If, for example, you mean that someone uploads information about a person "Jane Doe" and that person's parents, and grandparents, and generation after generation ... generations back, then whether the information presented accurately reflects those parents and ancestors or not, is really neither here nor there, as it is simply one person's theory as to who "Jane Doe" descends from. Whether it is well researched or simply based on someone else's published research does not alter the fact that it is based on theory, assumptions and official records. So for example while my own research validates my own oral history as to who were my Grandparents, all four as deceased, deceased long before DNA sampling became an option. Yes, I have their 19th Century NSW Australia birth certs, and the 8 NSW birth certs for their parents too.... But no matter how accurately I present my own research, it is afterall, just that ..... it is only research.
I simply cannot fathom what you are referring to when you write
" that having reached its earliest known ancestor - who has no known origins past or future - simply disappearing- but leaves a spouse and 4 children - is foisted onto another tree in an attempt to create a continuous lineage stretching back to the earliest BMD registrations in England"Does this mean you have the name of someone on a tree, say "Joe Blow" who is married to "Jane Doe" and they have 4 children ..... and you can only find the marriage for Joe and Jane, but no evidence of a birth or a death for "Joe Blow"
AND
you can find someone else's research where they have this same "Joe Blow" and they have ancestors for "Joe" right back to 1598 in England?
AND
you suspect that someone else has 'nicked' without permission, the information about Joe Blow's marriage and four children of that marriage and simply added it to their "Joe Blow"
If so, it seems to me that when you publish your research online, then by default it is open to be 'nicked', 're-hashed', 'mis-mashed' or otherwise misunderstood/mis-read and mis-interpreted to your expectations.
As to the legalities .... well, I am fairly certain that at least in Australia (I am in New South Wales, one of the nine jurisdictions that operate in Australia) that deceased persons cannot sue for defamation.
http://www.austlii.edu.au/au/legis/nsw/consol_act/da200599/longtitle.html I am sure there's RChatters who can provide details about defamation laws in other jurisdictions, as to me defamation is a tort.
Cheers, JM
