There are a lot of people like that. Mountain climbers. Surfers. Volunteer soldiers. Alaskan crab fishermen.
You don't see anyone proposing that crabbing be banned until we can develop automated machines to do the job, right?
We should start building on Mars without humans. If our machines can't do that yet, then we should invest in them until they can.
Right now the risk makes it too expensive, so the profit isn't there. Much of the work Virgin Galactic and the others are doing will lower the cost eventually. When it gets low enough, there will be people lining up around the block to become asteroid miners, etc.
Lack of willing people will never be a problem.
Not to say that there aren't large drawbacks (huge amounts of R&D, for example). Robot space travelers are also relatively uninspiring.