Oh, and it's not like Pd doesn't already write stuff in "~/Library", it actually does create files in "~/Library/preferences", so it's not like it's a sacred ground it can't touch... I'm still yet to understand what is the issue of Pd creating a folder in here...
Though I can agree it is a rather unusual place to go. Most softwares won't do it, and the reason this is being discussed is just that Pd happens to have that folder as a standard path in the first place... so it's coming from Pd for some reason. Now, I can see most softwares prefer to use other folders in the user area, outside this hidden ~/Library folder. For instance, audiosculpt went for ~/Applications. Max and Native Instruments went for ~/Documents. The place to install externals for Max is in ~/Documents/Max/Packages.
There's also the "shared" folder. I see Max and Native Instruments there too. So if you want to install something for all users, that folder seems to be the one to go.
So I'm now leaning on actually disregarding ~/Library as a good choice for creating and using as an external destination... not sure yet why there's a resistance it's a bad place to go... but if this is why, well, maybe a better option like these other folders would do.
That would actually work and solve thew other problems I was raising, where you can't navigate to the ~/Library folder if you want to add it in your "Path".
This is all for Mac OS of course, and we should check the options for other systems.
cheers