The way some people talk, you'd think that a relative of theirs had gone down on the R.101.
Had a reasonably large-scale, modern LTA/hybrid been built, tested and flopped operationally or technically, the case would be easier to make. However, a lot of reasonably sensible people and large companies have taken an interest in the topic, studied the problems and started to build hardware.
Most of the flops have either been due to fiscal exhaustion, or the customer walking away - and a big reason for the latter is that for the customer, the LTA is always a new area that competes for money with core activities, and consequently perishes as soon as money gets tight.
In the case of YEZ-2A, the Pentagon decided to give cruise missile defense to the Army, which favored aerostats - and that's how we got JLENS, which has the huge weakness of being very hard to relocate (lots of C-17s). LEMV could have been the best technology in the world but had a management structure that was
ed-up at the outset.
There are many ideas in the history of aviation that have been given much more money and allowed to prove whether they worked or not.