Who, exactly, is the "they" you are referring to? I don't think I've ever seen a single person on this forum say that if your dog can't free roam in the house you've failed as a trainer. That simply isn't true at all. The best trainers in the world use kennels all the time. It is, after all, usually safer and easier.
I also disagree with you saying that anyone that doesn't use a kennel is a bad owner. That is also not true. There are some dogs that absolutely cannot be kenneled. Some dogs, despite the owner's best efforts, continue to eliminate in the crate. Some dogs absolutely hate the crate, at no fault of the owner. Perhaps the dog was a rescue, and the damage has been done. The dog cannot safely be crated. I had one of those dogs. If he was crated, he would bend the crate door enough that there was a small hole and squeeze his way out. That is a surefire way to get your dog strangled. I have seen it multiple times. Also, if I used a plastic kennel, he would eat right through the plastic -- not safe. Your statement that 100% of the time kennels are safe is not even slightly true. Sorry.
To the actual OP:
I would probably not go. I'm sure it could be done just fine if your neighbor really can help out that much, but I would rather not put that stress on my dog. I know people that do it all the time, and everything is just fine in the end, but I think it would stress me out more than the dog!
There have been several on here that have written such. You either have luckily avoided them or are openly being dishonest. I've run into countless posters that berate people for balanced training or using proper gear, berate those that are proponents of crates or those that refuse to allow the dog to run things. If you don't coddle the dog and let it run the show and don't revolve your world around it you're a bad person and are abusive. And of course there are also quite a few that don't do that, absolutely.
At any rate, yes, anyone that doesn't somehow contain their dog or have a safe space from them free of any possible dangers is negligent. The home is a dangerous environment for dogs, especially for lengths of time like 48 hours. Even a well trained dog that ordinarily leaves things alone and doesn't cause mischief. Some dogs can't be crated since they weren't properly introduced and accustomed to it, true. But even in that case, they make kennels pretty strong these days. You don't have to get a wire or plastic crate, you can get a KENNEL that cannot be bent, cannot be chewed and cannot provide any risk to your dog. You can have an outdoor run area where the dog is fully contained. You can even simply keep them in a room without any furniture, without any carpeting or objects that can be destroyed/ingested. Whatever it takes to contain them. But allowing them to free roam a house for days is a recipe for a dead dog.
As I said, and you failed to comprehend, they are 100% safe 100% of the time when the dog is properly introduced, properly trained to use them and in extreme circumstances, when specific equipment is required such as kennels that cannot be bent, chewed, destroyed and are made of solid metal. Not wires or plastic. As I also said and you seem to have missed, I said if this is NOT the case for the OP and their dog is not properly crate trained, they CANNOT be left in the crate that long. So, read it again.
Different strokes for different folks, for some safety is just paramount. Life happens. That's why you start day one with a puppy making the crate a fun place, the best thing on earth and a place they spend the vast majority of their downtime for the first months of their life. Eventually life happens and you NEED it.