There are already a bunch of extremely expensive treatments for diseases and afflictions that affect a small portion of the population. Some of which are fatal if not treated. Should they be expected to just die because the treatment is as you said 'really really expensive'?
People need to appreciate how hard fraud is to circumvent in anything where government largesse is involved.
And you conveniently ignored my point on how what you suggested is essentially advocating for people to die if a treatment is too expensive.
I posited a hypothetical scenario, which can get extremely real if we start looking at real situations of benefits fraud, and asked you how we should deal with that. Are you really saying that the government should just pay whatever I want to charge for my service that doesn't work? If it does work, can I charge the government whatever I want to provide it?
What you're not understanding here is that this, and every other example of asking the government to do things, is manipulable by humans and thus is an adversarial process. Because the government isn't God, it doesn't have truly unlimited resources.
The original argument was never about 'should the government pay for fringe treatment that is not confirmed to work' but rather 'should the government pay for people who have fringe diseases or issues'. Your hypothetical scenarios and arguments have been drifting from the latter and into the former.