Why would you say that? People have been using Draino for decades with excellent results and no damage to their pipes when used as directed.
Annie-Xmas, you explain this better than I do, can you handle this query?
I read her response, but people use it successfully all the time.
Sure. But when it goes wrong, it goes really wrong, and that means $$$$. And, really, it doesn’t work all that well. AND, it’s dangerous.
Like I said, it should be used only by pros- and like Annie-Xmas said- pros don’t use it. That should give you a clue.
I can understand taking safety precautions, as I’ve already mentioned, but having used it to clear my shower drain on the recommendation of a plumber and found it very effective, I would have to say that as long as you follow the instructions carefully it should be fine.
I made sure it was thoroughly flushed away and diluted at the end.
There are materials such as Titanium that it should not be used for of course.
The OP doesn’t indicate and the question hasn’t been asked-is there a dishwasher? Dishwasher discharge lines connect either to a waste inlet on the sink tailpiece or a waste inlet on the garbage disposal, both of which are above the sink J-bend. Food residue, darkness, and warm water added together form a good breeding ground for stinkitude, particularly if the dishwasher is run infrequently, thereby allowing science projects to ferment in the pump body. 
Nope, no dishwasher.
The main dangers are damage to skin, to sinks, to pipes, to anything that can be damaged by caustic liquids. It is not a safe thing to have around the house.
Plumbers hate it because people call them when it doesn’t work. Like I said above, what do you do with a pool of caustic water.
I once saw a pipe that a plumber had to remove because it was clogged with a nasty green soap caused by the combination of drain cleaning lye and grease.