I think that a lot of people outside of schools have no clear idea of what a day is like for a teacher. If there are 6 periods a day, and I have 1 'free', the chances are excellent that the 1 period will not actually be free, I will have to cover a class for an absent colleague, or take calls from SMT, or sort out behaviour issues in other classes in my department, or have pupils at the door wanting passwords changed/sent as they were misbehaving/ can't remember what class they should be in, etc etc. I have been teaching many, many years and cannot recall a single 'free' period that I've not been disrupted by something at least once.
Staff are expected to do break and lunch duty, expected to run lunchtime and after school sessions for revision, homework, exam prep etc etc - so the point about the 8-6 isn't that no one else does it, its that for teachers there is no actual time to do all the other stuff in those hours. The last few years there is the added expectation that staff offer exam prep in the October and Easter holidays. For sure they can't force us to do that, but if you ever hope to get promotion, or apply for a job elsewhere, or even come through one of the QA observations/learning walk reports without a scathing 'not a team player' type comment you're going to be doing those.
There's no 'quiet time' to do marking or planning or report writing or whatever, and unlike people in industry we don't even get paid til '5 or 6pm'.
Add in the governments revolving door of curriculum changes (just who do you think rewrites those courses, usually in a stupidly short timescale). I mean Scotland was a prime example - they launched CfE National 5 courses 5-6 months before they actually published the course specifications so we got to 'teach' a course that hadn't even been published from June to December and just hope we were covering the right things. The government kindly allowed the delay of the Higher courses the following year, though in reality in a great many schools the management insisted that we deliver the new (again not actually finished) version of the course. Some subjects were changed (hugely changed in some cases) every single year for the first 4 years. Keep in mind there is no 'down time' during the school day to rewrite these courses.
Lockdown has been a great example - we were expected to teach live, online lessons as per our usual timetable (fair enough), but our twice termly staff meetings went to twice a week (sometimes every day!), we had to do 4 (yes really) different types of tracking, weekly and for every single pupil had to add in a comment about what we'd tracked. Weekly.
All the while rewriting the courses so they worked online, writing new materials to make up for the lack of in class discussions and demonstrations, pre-recording lessons, contacting pupils who hadn't been engaging with lessons to offer extra help and trying to sort out the plethora of IT issues that came up 'I can't search for Chicken Breast Miss, it came up that I tried to access porn...!!!' And some tasks that can be done fairly quickly in a classroom (going over a task from a lesson) now takes an hour as you have to individually mark and give feedback for each pupil
No one is saying at all that other jobs are not stressful or have stupid workloads - they absolutely do.
What we are saying is that teaching also has a stupid workload and while the media like to make out we all work 9-3 and get paid loads to do nothing and have half the year off, the reality is very different.
I think what gets teachers backs up (certainly mine anyway) is this idea that we are all lazy work-shy idiots doing a crappy job because we're not capable of hacking it in 'industry'.
Other similarly overworked and underpaid professions are vaunted as 'angels' and 'heros'. It only seems to be teachers that are viewed as workshy and lazy.
If lockdown has shown anything from the cries of 'open the schools!' it should show how crucial the profession is, and yet there is still thread after thread of how little teachers do, how long their holidays are and how they have no clue what life is like 'in the real world'