Can you imagine someone breaking down/punctures? The lot of you have to hang about waiting. You can not pull up on the side when you want to or have spontaneous change of route should you come across a road you fancy the look of. (PS. I’ve never been on one of these and as such I only imagine the worst, I might be totally wrong though)
I do generally try to avoid internet arguments but, honestly, why on earth would you offer an opinion on something of which you have no experience? You ARE completely wrong, because you simply do not know what you're talking about - which you admit. I just don't understand why you'd slag something off based on nothing more than prejudice, preconception and ignorance... What is the point?
Group tours aren't for everyone (they're not really my thing) but I have done a fair few, with different operators, and I do know how they tend to be organised. Nobody should be put off doing one, if they're interested in the idea.
First, no two companies are exactly the same. However, none I've been with has a problem if you want to do your own thing, stop when you want, detour where you want - as long as you're confident that you can get to the hotel without being guided. The good ones will check you're happy and give any tips ("look out after the church in X town as it's easy to miss the turning" or "There's a good cafe in Y town") before you go your own way. But all of them understand that there's no point dictating to riders: for it to be a good holiday, people have to have the freedom to do what they want. If you are riding in a group with the tour guide and you peel off on your own, you shouldn't get to 6pm and then decide to call the guide to say "I'm lost - come and find me" – though it happens. I know of one tour guide who went out to rescue someone who'd done this (and got back to the hotel after 9pm).
All tour operators encourage people to ride at their own pace (it's vital for safety) and most of the ones I've ridden with try to avoid having all the bikes riding in a single big group. It might be a bit more of a big group on the first day, but most trips pretty quickly break down into groups of two or three bikes riding together as people get to know each other and settle in to riding with those who go at a similar pace. The bigger group tends to come back together at stops – you see other bikes from the tour parked up at a cafe, so you stop and join them - and in the evenings, for a beer in the bar and for the evening meal. Sometimes a larger group sticks with the guide, but I've only ever been on one tour – in America – where the organiser wanted to run it as a single giant column of bikes with a guide at the front and another at the back (and even then I was able to jump the fence and do my own thing whenever I wanted).
As for what happens if someone breaks down/has a puncture... well, if it's you that gets the puncture, I dare say a bit of assistance would be welcome. But no tour operator will ruin everyone else's day by making them sit around while they fix Johnny Handbrake's puncture. Most will just quickly make sure the rest of the group can carry on safely to the destination while they stay back to assist the rider with the problem. Sometimes one or two other riders will offer to stop and help as well (exactly as if you're riding with a mate at the weekend: you wouldn't just sod off and leave them if they had a puncture).
But the rest of the tour participants don't have to scrap their day of riding because someone else has broken down. There is a bit of Benthamism going on, with the needs of the many outweighing the problem of the one - so while a tour operator will do what they can to help whoever has the problem, they have to look after the other travellers. Some trips even have a support crew (with a van for stricken bikes) that will "sweep" the route and help riders having a problem, while the guide continues guiding. I did one trip where a guy crashed and the tour operator not only picked his bike up but also took it to a local garage where the broken bits were replaced and they hammered the panniers back into shape so the chap could keep riding; he was back on the road next morning. That support is one of the big attractions of a group tour for some riders who haven't been abroad on their own before. But all of the tour companies I've travelled with require riders to have suitable breakdown cover when booking on, and if it all goes wrong the rider has to call on that – not ruin everyone else's holiday.