The liquid oxygenation explanation above is awesome. I knew that exposure to oxygen alone never ruined my beer, but never really thought about it until now.
All I can share are me experiences. I've done 30+ 5-gallon batches in buckets, and about half of those were semi open fermentations. If you haven't heard of it, search for "open fermentation" or do a Google image search to see it.
I plug the airlock hole on the bucket lid and loosely place it on top of the fermenter without snapping it down, leaving it that way throughout the fermentation. I repeatedly pull the lid off to check if the krausen has dropped, harvest yeast by skimming the top, to take gravity readings, to add and remove dry hops, take taste samples, check for clarity, and add gelatin. When I don't add dry hops directly into the beer, I use a hop bag. Once I'm done dry hopping, I pull them out and squeeze all the beer and hop juice out, which causes a bit of splashing. I also take samples with a wine thief, which causes a bit of splashing as well. Even with all of this, I have never had oxidized beer or a single infection. As long as whatever touches the beer is clean and sanitized it will be fine. It's not like I spray StarSan on my hands when I squeeze the hop bags either. I just wash them well with hot water and soap, and I don't dry them with a kitchen towel for sure.
Like I said, I have no experience with oxidized beer, but I imagine it would require a lot of vigorous splashing for it to turn bad. And as long as nothing dirty is going into the beer, infections shouldn't be a high risk either.
And just so you know, I ferment this way often because I use a compact fridge for temperature control. It's easier than having to pull the bucket in and out of the fridge to pop the lid off. This way, I can leave the bucket alone and just pull the lid up to do whatever I need to do. When I ferment in my pantry, I do snap the lid on and use an airlock because our trash and recycle bin are in there as well. There's more of a chance for things like fruit flies that may be able to squeeze in under a loosely placed lid.
It's home brew and its your beer. Do what works for you.