"If we 'lost' Amazon we would presumably still want tat. It's hard to see that there would be a loss in either jobs or taxes"
Really? We want but because its cheap, available, easily checked up on and reviewed and of course this employs not just the many people working in efficient warehouses but also the delivery companies/logistics/etc feeding off the increased business. We would lose jobs and tax's and considering how easy Amazon make it to order from the world it would have a large impact.
"Doesn't mean I don't think that the world might be a better place if I got all my tat from a local neighbourhood tat shop"
At greater price? Less choice? Why does a can of beans cost more in a small shop? Because it costs more than a supermarket. Amazon have gone much further than that. Local shops may not stock what you want. Nor the numerous alternative outlets. If tat was better bought locally we would, but we prefer Amazon because its better, cheaper and has more choice.
"one that might pay rent to a landlord, fair wages to it's employees and tax to the government."
They do. They put their warehouses where its cheaper. They pay wages equal to what the job is worth (or nobody would turn up). And they pay their tax's otherwise they would be jailed for illegal activity.
"And one that might reinvest its profits buying goods or services from its neighbours, rather than squirrelling it away in a tax haven."
Actually one of the complaints against Amazon is the lack of profit, which is because it gets reinvested into growing the company.