Do you remember the old cross-channel hovercraft. The pilots operating them had to have an ATPL, which is clearly ridiculous. Had they become more widespread I'm sure someone would have eventually waived the requirement. Likewise for drones. If they can be demonstrated 1) not to be habitually sharing airspace with manned aircraft and 2) to be capable of avoiding collisions on the rare occasions that they come into conflict then their utility is compelling enough that the world will adapt itself to them.
Current legislation is geared towards the management of manned aircraft; this will have to change in the same way that legislation regarding newspapers has had to adapt to the internet over the past few years. However, there are many different jurisdictions when it comes to airspace and, ICAO notwithstanding if one country doesn't eventually adapt to enable drones, then another will. As they are clearly going to be big business, governments will want to cautiously enable research and development to happen on their soil so that they get a slice of the action, so there's a lot of impetus to enable change.
What does it mean to operate a drone? Ultimately it's going to boil down to the end user specifying two sets of co-ordinates: a pick-up point and a drop-off point, and putting something in it. The rest will be arranged by software which will be written by people who really understand what they're doing. In a sense the 'operators' will need little direct oversight. Maintenance people will really have to understand what they're doing too: but drones can be mechanically simple with a lot of redundancy.
I agree liability is an issue, but you could say the same about self-driving cars - which are clearly on the cards and where it's likely to be a far bigger issue: the average drone crash will squash some plants in a field; the average car-crash is much more likely to actually hurt someone. I used to work in a hospital where if you were writing a letter about patient A but then looked up blood results for patient B, it would put patient B's name on the top of the letter, then change it back to patient A when you came to print the thing out. It often seems to me that computer programmers seem to get a free-ride when it comes to liability issues!
Amazon seems to be taking reasonable, baby steps operating first of all in the countryside where the consequences of an accident are likely to be minimal. There are also companies delivering medicines and blood products in Africa. Ultimately, the objection to your objections is that drones are already flying around doing useful stuff in several countries. With Bill Gates' caveat that people overestimate the short-term impact of technologies and underestimate the long term impact, drones are inevitable.