Weed or not weed?

Vera has just posted about, among other things, her beautiful bluebells. I saw some lovely ones on the weekend, at Warburton.

bluebells, purposely planted

Last week I saw some onion weed (I don't know if it has a nicer name, that is just how I know it.) Doesn't it look a lot like the bluebells?

onion weed, also spreading a lot

more onion weed

yellow oxalis - gorgeous but everywhere 

Many of the so-called weeds have survived the drought and helped to prevent major erosion in our local parks, so they have actually been wonderfully useful.
I am coming to the opinion that if it is indigenous to Earth, then maybe we should leave it alone.
Then I see some plants strangling others, making monocultures, causing rashes, giving us headaches and hayfever, etc.  Some of them are imported and some are indigenous.  It is getting harder and harder to believe that places can have fully indigenous flora - and maybe we shouldn't stress about it too much.

Ivy growing on a tree fern stump.

wattle -aaargh!!! (aka Acacia) - major allergy source, at least for me

It is all so confusing, what to plant, what to pull out.