I prefer available light, but admittedly didn’t really get the whole flash thing when I studied at uni. However, I had a kind of revelation at one point, realising that available light is just like a whole lot of soft boxes, fill lights, spots and etc. The window behind me is a huge soft box, the lamp next to me is a little tungsten spot light & the huge white wall is a brilliant reflector.
Light is light is light…so as a photographer; whether you use available, flash or a flood light for builders; you still need to think about the lighting ratios and evaluate the intensity, colour, texture and general quality of the light around you.
I do think that flash can sometimes be intrusive and so I don’t often use it for portraits, but if used properly (and it can be used properly) it doesn’t take away from the mood or feeling of a scene/story. We are already making so many choices from the camera, iso, focal length, aperture & shutter speed to framing, cropping and general editing, so that we are already extensively manipulating the images. Important I think is how you approach your photography. And if you are sincere, that will show. A good example of how flash can work really well is Brice Gilden’s work: http://www.artnet.com/artists/bruce-gilden/