want to know why the above is a bad idea.
i am not going to try any of this but i would just like to know, why we should not breed ts this way, i have been wondering for a long time now.
thanks in regard.

Source wiki

"Inbreeding is the reproduction from the mating of two genetically related parents, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is called inbreeding depression."

"A crossbreed or crossbred usually refers to an animal with purebred parents of two different breeds, varieties, or populations. Crossbreeding refers to the process of breeding such an animal, often with the intention to create offspring that share the traits of both parent lineages, or producing an animal with hybrid vigor. While crossbreeding is used to maintain health and viability of animals, irresponsible crossbreeding can also produce animals of inferior[clarification needed] quality or dilute a purebred gene pool to the point of extinction of a given breed of animal."

and a hybrid is the name of a offspring from crossbreeding parents.

You also have to know that there is not much on arachnid inbreeding, as more studies must still be done.

oh yes, so a lot of people bought b.vagan slings, lets say they mature in a year from now and i put my male on breeding loan and someone takes it (but has one from the same batch that also mature) what would happen if we do breed them?

They'll breed and likely produce offspring..

I've read somewhere that you could 'inbreed' for up to 7 or 8 generations without having any problems.

The problem in South Africa is that hundreds of slings of the same specie was imported. So most of us have B. smithis that likely came from the same batch (which was imported). Now our males and females mature and we pair them, but they are actually related.

Most of our tarantulas are related in some way or the other...

and most probable too!

Breeding T's from the same egg batch would not generaly pose a problem
since T's could do this for a number of generations before this become problematic.

We don't support crossbreeding between different species as our hobby is
already under pressure from the nature people (no offence) so
inbreeding would just aggetate alseady irretated peole in the wrong places.

Secondly we like the T's the way they are, made by nature so why go
and bother with the way nature has done it. We love them the way they are
and that's the final answer, no correspondece will be entered into.