In fact I can actually do SMD soldering without it. The point at which it makes things easier is rework.
Anyone can do SMD soldering without extra flux... by cleaning off the tip of the iron, putting it on the joint, and then feeding solderwire into the joint. But then you have to tack a pin, somehow, because the SMD parts don't stay put by themselves.
The point at which it makes things easier is rework.
Sure, it can be useful for rework. But in general, the more SMD you do, the more you might realize it's not religion or personal preference. It's just a matter of efficiency. Using flux, appropriately, you can do certain things faster and with less effort. When hacking together a circuit one bit at a time, making things up as you go, adding one component every ten minutes, it doesn't matter as much. When you design a large board in CAD and populate it, flux might not be strictly necessary... but you might be doing it the hard way.
I can solder anything that I would ever need to solder with just a radioshack firestarter (and a file) and solderwire. I could take pride in that, I suppose. But to suggest to someone that they don't need to bother with flux is insanity.
Before I finally ponied up for my first bottle of proper rosin flux, I used the plumbers flux from the hardware store. (It took some years before I learned where you shouldn't use it; even cleaning with hot water and a toothbrush, you can't use it on steel/iron without causing rust!) You can buy 4 oz (or maybe 8 oz?) bottles of rosin flux from Alphametals or from MG Chemicals. That will last a good while for the average joe. But even a 1 L bottle of MG RA is only 25.00.
Cost is another thing to consider. Before I started using flux, I wasted a lot more solder, adding it to coldish joints just to get the flux out of it. Cleaning the iron tip from cold solder. A significant portion of the solder I used ended up going into the trash, either swept off the floor or out of my brass wool tip cleaner. At $12-20 per 1 lb roll of solder, and 25.00 for a liter of flux, flux ends up saving money. A liter of RA flux can get you through 10-20 lbs of solder, potentially saving more money than it costs. Unless you are buying the $30.00 syringes of special sauce.