I suspect that people are talking about very different things on this thread, and that this is the root of much of the disagreement.
totallybewildered is arguing against the installation of very managed garden spaces in rich ecosystems, and it is good to recognise that there is a point beyond which this type of planting anywhere becomes very damaging. We don't want Sights of Special Scientific Interest covered with those really bright garden primulas, for instance!
However, that's absolutely not what most of us are advocating. Turning a monoculture grass verge of grass which is mown before it flowers into a veg garden or even a wildflower meadow has benefits to both the community and to wildlife. I would point to the work of Nigel Dunnett, who has done some amazing 'wild' planting schemes that turn what is essentially quite unusable outdoor space into something both more biodiverse and more beautiful than plain grass, which doesn't do much for anyone.
Plants like aquilegia self seed absolutely everywhere of their own accord. I highly doubt those struggling to reduce their populations are the victims of guerilla gardeners - it's a plant that doesn't need much help. Fortunately, it also has an amazing propensity to hybridize which means that you often get an incredibly varied group of plants in your garden from those little seedlings. In mine, a whole range of pinks and mauves and whites have arrived without me having to lift a finger! And that's leaving aside the stunning cultivated varieties that you can buy. If you have wild aquilegias, it's therefore often worth waiting for these to flower so you and the bees can enjoy the many different colours and shapes they produce - you might have something truly surprising in the mix! Then, if you want to keep the population in check, you can cut them down before they set seed. However, if there are any growing around you in the neighbourhood, they will find their way back in! So rooting up any cuttings you don't want throughout the spring and summer is the only real way to get rid, and even this won't be permanent. Nature can be amazingly fecund sometimes.
waves at everyone regular from Berlin