Respectfully, history documents innumerable instances of the fact that photography is art. To use just one example, copies of William Eggleston's "Greenwood, Mississippi" (aka The Red Ceiling) are in the permanent collections and have been exhibited at the Museum of Modern Art (NYC) and the J. Paul Getty Museum (Los Angeles). Prints have been exhibited at the Whitney Museum of American Art (NYC), the Victoria & Albert Museum (UK), and many other museums & galleries around the world. Eggleston's solo exhibition at MoMA in 1976 is widely recognized as the ascendance of color photography to a position alongside black and white as an artistic medium. Sotheby's has recently estimated the value of a print at between $150,000 and $200,000.
By any rational metric - being exhibited as art, reviewed and praised by critics, historians, and large sections of the public as art, appraised, sold, and collected as art - Eggleston's photography is art. The same can be said for many photographers whose works have passed the same threshold over the last 150+ years.
To deny this is no different from denying that any accepted medium (painting, sculpture, dance, music, architecture, etc.) is art. If you'd like to discuss or debate which photographic artists or photographic works of art are the greatest in history, that sounds like a fun thread. If you'd care to discuss or debate Eggleston's standing - or color photography in general - as near the pinnacle, middle of the road, or somewhere else in the Pantheon of contemporary art, that also sounds like a fun discussion.
But to deny that photography is art in the face of the historic fact to the contrary seems rather a waste of time.