Out With The Ferns, In With The...Oxalis?

My working definition of a weed is any volunteer plant that I am routinely asked to remove from a given garden. Since I have no garden of my own, the only weeds I can define for myself are the ones tenacious enough or of seed omniscient enough to sprout up in my numerous container plantings. I am not fond of these weeds, as I'd like to think one of the few benefits of not having a garden would be an absence of menial maintenance tasks such as weeding. Therefore, I have no great attachment to the grasses, dandelions and liverworts I disgustedly pluck from my pots when they begin to obscure my beloved plants.
It is considerably more difficult to align my weed definition with my gardening conscience when I am in a certain client's garden. Especially when said client is instructing me to "dig out those pesky ferns" because they are "everywhere". The ferns in question are two or three lovely western sword ferns (Polystichum munitum) of modest size and excellent health which, despite my being able to count them on one hand, are apparently everywhere. Now let's never mind that these are native to this area and so were springing up as "weeds" eons before humans slapped up their poorly-proportioned million-dollar ramblers-with-a-view on the site. Let's instead consider that this client puts her foot down on a few sword ferns, branding them weeds, while all about her sprout the immortal heads of at least a dozen terribly invasive species which truly are everywhere and which she herself introduced into her garden. Oxalis, Alstroemeria, Aegopodium, Ajuga, Digitalis, Aquilegia (not the native), and Angelica abound, to name a few.
I propose that we show some tolerance for sword ferns (which, by the way, are quite easy to remove and relocate if necessary) and show some discretion in the aggressive plants we willingly bring into our gardens. Future home-owners and gardeners alike will thank us.