Yes, as it is all that simple, isn't it? Ok, let's start with the shops. On top of the staff you mention, there are relief managers, regional managers, area managers, studio operators et al. Then you can think about the internet/call centre side of things; cut out betting on horseracing and turnover would be cut by around 50%, so yet more of the staff from there would have to go.
Oncourse there are most definitely thousands of people employed in the betting industry and your posts are demonstrating clearly that you don't know the full extent of the industry. Each pitch has around 4 or 5 staff; plus reps; people 'putting on'; Betfair/Betdaq reps; then you've got PA staff - both oncourse and in studio - as well as SiS/Turf TV staff - both oncourse and in studio; ring inspectors; technical staff; betting security staff.....need I go on?
Anyway, not a lot of point going round the houses with this one since it's never going to happen. I was hoping that you might come around to seeing how unworkable the whole idea is, the UK already has a robust industry in place which doesn't need decimating, creating thousands and thousands of unemployed, on a whim.
I'm also quite disappointed that you seem to think that putting so many thousands of people out of work so you can go racing cheap a few times a year is only a 'downside'. I'd respectfully suggest that were you to have a career that wasn't guaranteed for life - with a staggeringly good pension scheme to boot - you might have a bit more respect for other peoples' livelihoods.