Self-checkouts are not in principle unethical. If it means that the supermaket is now more profitable then the total GDP for the country has gone up slightly, which means there is slightly more money for us all to share. This could mean that the welfare state is strengthened or could help towards the implementation of a universal basic income for all citizens. This would mean that the person who used to be sat on a till all day every day can now, more easily, pursue their dreams. That would be a good thing.
Of course, that's not what happens. The self checkout is there to increase the profits of the supermarkets and the dividends of the shareholders.
Ideally, we would have both self-checkouts and a government which actually had the interests of the whole population at its heart.
Over the next decade, it's likely that entire industries will shed their workforce. Logistics and haulage for example. This won't mean that there's less money floating around for us all to share. So it means a massive opportunity exists to release millions of people from drudgery.
In the past when similar changes in workforce have occurred, the result was that new jobs and industrys were invented to keep everyone busy - hence call-centres. I sadly expect that the same will happen this time.