I think the cloning example is a good reference point here.

IIRC, human cloning started to get banned in response to the announcement of Dolly the sheep. To quote the wikipedia article:

  Dolly was the only lamb that survived to adulthood from 277 attempts. Wilmut, who led the team that created Dolly, announced in 2007 that the nuclear transfer technique may never be sufficiently efficient for use in humans.

Yes, things got better eventually, but it took ages to not suck.

I absolutely expect all the first attempts at brain uploading to involve simulations whose simplifying approximations are equivalent to being high as a kite on almost all categories of mind altering substances at the same time, to a degree that wouldn't be compatible with life if it happened to your living brain.

The first efforts will likely be animal brains (perhaps that fruit fly which has already been scanned?), but given humans aren't yet all on board with questions like "do monkeys have a rich inner world?" and even with each other we get surprised and confused by each other's modes of thought, even when we scale up to monkeys, we won't actually be confident that the technique would really work on human minds.