I hate them.
Their main purpose is to train us to do the job of the checkout staff. Once the percentage of "self scanners" is high enough, the supermarkets can make a significant proportion of their checkout staff redundant.
Every time you self scan, you are helping to do checkout workers out of a job. It's not the most exciting job in the supermarket, but it's what a lot of people do to earn a living.
Stop taking their jobs.
Fight back against the self scanners.
Tell the supermarkets ... we are not going to let them crap on their workforce, even if they do disguise it as "quick and convenient"
If supermarkets want the checkout process to be quicker and more convenient, they should give jobs to more checkout staff, rather than trying to put their existing ones out of work.
Keep checkout staff in a job. They need you to use them.