There are very stringent requirements that animals have to meet in order to start the domestication process - spiders do not even come close to meeting any of those requirements. Neither do snakes, lizards or any other herps.
There is a HUGE difference between domestication and being 'tame'. Some animals have a much higher tolerance level for human interaction than others, but that does NOT make them domesticated, or even tame for that matter. Going hand in hand with that is the fact that they are not able to kill you.
For an example - a corn snake is no more tame or domesticated than a rattlesnake is. It is just that one is capable of killing you and the other isn't. A snake that is small can't kill you either, but if it is allowed to reach it's full, natural, size - it can very easily kill you. We have all seen the news stories of people being killed by their 'pet' snakes and that is because they are NOT pets - they are wild animals and will kill you under the right circumstances. They will never be domesticated and they will never be tame - they are wild and unpredictable.
Tarantulas will not kill you as their venom is not potent enough. In most cases it is not even potent enough to kill a cat or a dog. But that doesn't mean they are any more tame that a Recluse would be just because a recluse can potentially seriously harm or kill you. Tarantulas can, and many will, still bite you without thought and it is not a fun thing to experience. Their fangs can do a lot of mechanical damage to nerves, and tendons, and you don't want to be bitten.
Don't mix up domestication with captive bred - the two things are WORLDS apart and are not synonymous by any stretch. And don't think that their tolerance level is any indication of tameness either - they are unpredictable and, an otherwise calm and docile animal, can easily harm or kill you without provocation.
Many tarantulas, including a species that I have had, are on the endangered (CITIES) listing due to one factor only - the pet trade. These creatures can't afford the pet trade to have that effect on them because other factors are already making sure that they ALL end up extinct long before they should be - environmental destruction, drought, lack of food, loss of habitat, etc., etc., and the list goes on.
We all have a choice whether we want to be the nail in their coffin, or not, by supporting the pet trade. I, personally, will not contribute in the future and will forever advocate for them being left in the wild where they belong.