This is the dilemma for me - I can see and understand why cyclists do this- I truly get the point. Accepting that, though, motorists seem more hostile to other road users, and perhaps especially cyclists, more now, than ever.
Painted cycles lanes, and separate cycle paths haven't helped - because they just engender that perspective that cyclists shouldn't be on the road, and actually be traffic.
I also think there is a contingent of cyclists who often behave in a bloody minded way, just to make a point - I say that as somebody who normally defends cyclists in the discussed altercations with other road users. Some of me thinks I get their battle - that they are metaphorically stood on that wall so I don't have to - but then knowing human nature, I suspect many aren't doing it for any particularly noble cause.
All the same, cyclists have actual rights to be using the road - something that only pedestrians and horse-riders can otherwise claim - motorists are merely permitted a qualified privilege to drive vehicles on the road - that can be removed at any time, and often is.
In recent years, I've come to hate cycling on the road - and it pains me to say that, having spent so many years, previously, cycling on road (as well as off). I try and cycle with a mind to be assertive, yet not provocative - mindful that consideration is a two-way street. All the same, though, it really doesn't turn out to be received as I'd intended, and I rarely find the spirit of compromise is evident with most motorists I encounter, when cycling.
I think the primary position sets a marker about being treated as traffic, but at least in my experience, perhaps too much of a presence that will comfortably be tolerated. I try and strike a balance - because the other option of driving in the gutter is effectively what you'll be treated as - and give myself some space from the kerb, but not so much as to entirely dominate the lane. All that said, sometimes, it's not possible to do that without occupying more space than some motorists will think you need - and that leaves us full circle with one of my earlier points about no longer enjoying cycling on the road and being part of traffic.
I suspect, thinking back, in earlier years of cycling on road, before as much knowledge and discussion brought on by the internet years, in my ignorance of (probably) cycling in or near the gutter, I was probably considered a lot less of an inconvenience to motorists I encountered.