A little structure...
Interesting topic, but it would make sense to be more specific before making sweeping generalizations and recommendations.
1. Not all dinghies are alike (for instance, I have never before heard of a "dingiu!") There are inflatables with soft bottoms, RIBs, hard-shell dinghies, hard-shell with tubes, and so forth. Lengths vary 7' or less, to 12'+. Of course, I'm ignoring the enormous RIBs and even express cruisers that some very big yachts bring along. Motors range from tiny weed-whackers to 15 to 20HP 120 lb.+ monsters. One recommendation for towing or stowing does not fit all!
2. Towing with the motor on. I have an 11' RIB with a 15HP two-stroke Merc. I have towed this thing all over the place for eight years, in thunderstorms, 10-15 seas with 35 kt winds, through breaking surf leaving the harbor (where I saw the dinghy behind, completely out of the water) - and we have never flipped it. It is extremely stable right-side-up. I recognize that some dinghies are not as stable, and warrant motor removal. Not all. For some it may be impractical, difficult, inconvenient, or even dangerous to lift the motor on and off every time, especially ones with heavier (100 lb.+) motors like 15 HP four strokes (dinghy davits notwithstanding).
2a. "Bring it on deck before entering a Marina." I don't get this. Are you supposed to heave-to and order the crew to "recover all small boats?" What if there's big weather? When entering port we just shorten up the tow enough so we won't wrap the tow line if the dink catches up.
3. Bridle. RIBs don't require a bridle. Use the towing ring.
4. "Open the drain valve so water will not accumulate in the dingui." Don't get it, there must be some context for this that I am unaware of. When I pull my dinghy onto the dinghy dock for storage, yes. In the water? No!
5. "Don't tow in the sea." "Chances are it won't tow right." I don't get this. If you spend any time on the water, you will see the vast majority of folks with dinghies towing them. Rarely seen on deck on coastal cruisers up to 50 or so feet in length. Properly rigged, a dinghy can tow fine, unless it's just a poor design. I wouldn't want to tow an Optimist very far. I've seen everything from 6' fiberglass dinks behind C-27's to 36' express cruisers behind mega-yachts, to ocean-going barges behind 100'+ tug boats in my cruising area.
6. Offshore, agreed, don't tow one if you're likely to encounter big seas, it may end up on board unexpectedly.
7. Be prepared to cut it loose in an emergency. We have emergency knives attached to the stern and bow pulpits (tie-wrap the sheaths). Once the emergency is over you can go find your dink. Others will likely help you.
8. Here's a big one for me: attach the dinghy tow line with a link, like a small safety snap, that will break under extreme loads. Even a light (3/8") line won't part, and will either damage the dink or drown (submerge) it if something gets between your boat and the dink. Even large normal towing loads won't break a small safety snap. Think of it as a fuse.
