You're always going to get opinions at the extreme ends of the spectrum on a forum like this because most of the posters will either be here raving about or ranting about their experiences. It is the nature of the beast. In the real world outside are millions of people in the middle, doing pretty well or just muddling through who never post on a forum.
There will be posters who want to protect 'their' breed by warning people off them and just as many saying how wonderful is 'their' breed and to ignore the naysayers.
The 'hate for cockapoos' is not about the actual dog, it's about the cynical way most (not all - but most) are bred and sold, with no regard for the welfare of adult dogs or resulting puppies. A number of these pups have the most appalling trips to the marketplace. All the horror stories are true, sadly. Working at a training school I can also confirm that while many are delightful little bundles of fluff, there's a good few which are not easy at all, being prone to hyper (at times almost manic) and/or fearful behaviours.
The above also applies to labradoodles which have the added caveat of often turning out to be very large and boisterous. Even the guy who first deliberately made this cross to train as 'hypoallergenic' guide dogs wishes he hadn't done it. Full bred poodles didn't adapt to guiding work so to get a non-shedding but still capable guide dog he brought in the labrador blood. The experiment was a failure in that only one of the three pups born proved to be hypoallergenic and biddable. Although that one did work as a guide dog until retirement, the breeding was never repeated. Nobody wanted the other two pups initially, although 'failed' guide dogs are normally highly sought after, so a bit of clever marketing named the 'labradoodle' and here we are.
Of the various 'poos and oodles' the calmest and most sensible seem to be the cavapoos. They have similar appealing looks to the cockapoos without being as hyper; but then in all conscience, purebred cavaliers have dreadful health problems for which a simple crossbreeding does not guarantee resolution, so on welfare grounds I wouldn't want to recommend those, either...
Other problematical breeds from a risky or badly bred perspective are French bulldogs, bulldogs in general including the English, American, pocket, xl and xxl bullies, pugs, and chihuahuas (and their crosses). Especially the so-called 'rare' colours, which have usually been banned from KC registration on health grounds because of the genetic disorders which often come with the colour mutations. Some French bulldogs in particular seem to be showing poor temperament, being 'snappy' if not actually aggressive and for some reason many are very difficult to toilet train.
Which is not to say that there aren't many great family dogs amongst these breeds/crossbreeds. But it is much harder now than it used to be to find those good ones amongst all the poor souls being churned out and trucked all over Europe to the detriment of everyone involved except the people making the money out of them.
It's a scientifically proven fact that most dogs do not like being left alone at home all day; there have been studies involving the measuring of cortisol (the stress hormone) in the blood which showed that even dogs which appeared sanguine about being alone on the cameras filming them showed raised levels indicating stress response. As in people, some dogs cope better than others with stress. Many really suffer. Those 'funny' internet memes showing dogs next to demolished walls and broken doors or destroyed window blinds saying 'thank doG you're back!' are not funny for the dog. Many, many dogs end up dumped and in rescue because of separation anxiety and it's the main reason why rescues won't home to full time workers because they know it's highly likely that the dog will bounce right back, however much the adopters say they are willing to do the sometimes long and frustrating training necessary to rehabilitate the dog and that is a three-way lose-lose situation. Dogs can be accustomed to being left home alone for a few hours at a stretch, but not a typical city commute day or a twelve-hour shift plus travelling.
Dogs and children do not always get on. That's a bare fact which has a lot of ifs, buts and maybes dangling off it. If a rescue homes to a family with young children and there is an incident, they will have that incident on their conscience and will likely be castigated as they 'should have known the dog was unreliable/vicious/not good with children', even though once the dog has left the rescue they have no possible control over the dog or its treatment in the adopting household, however in-depth their home check. For safety most rescues therefore have a lower age limit for the children of adopting families. The oft quoted solution of 'getting a puppy so they can grow up together' can also be problematic as the puppy will grow and develop much faster than the child so unless there is close supervision and proper instruction of both puppy and child as to how to behave around each other, things can come unstuck.
Same applies to cats and other animals in the home. Some dogs will never settle with a cat or other pet in the house; many will, but you're not going to know which you'll get until you get it. Do you want to risk losing your resident pet or having to rehome your new dog?
All it comes down to is people trying to make others aware of the possible pitfalls and issues so that they don't take lightly something that could be a ten to twenty year commitment, encourage a vile (and illegal, in many cases) puppy trade or cause harm to their families and pets. People get very blunt on here because in many cases the same questions come up time and time again, often starting with 'I've done my research and...', a statement that often reveals more about what the poster doesn't understand than what they do.
Side note to ParanoidMarvin: I've just read your thread again and can't see where anybody is being hostile. When your thread was asking what training people did, stating strongly that you want to get it right, the breed of the puppy you're getting is a pretty valid point. The key factors for successful training are genetics, education and management and the first greatly dictates how you handle the other two.