Denial of service is not an "imposition" of anything.
Personal freedom includes the right to control of one's own private property (in this case, one's own business). Besides, no one has the "personal freedom" to force others to serve them.
I firmly believe that the government should be able to regulate the smooth flow of commerce. There is nothing good or efficient about a market where you have to deal with a player who might not sell you
X or
Y because "RELIGION."
What happens when the only gas station in town refuses to sell you gas? If the only restaurant or grocery store in town refuses to serve you? The only pharmacy in town refuses to fill your birth control prescription? Or, what if your ability to obtain that birth control prescription simply depended on whose day it was to work the counter?
You can say that, OK, a free market will weed this out. Would it
really? Passing a bill would be seen as the government implicitly OKing discrimination, giving the country a green flag to start doing it again. The free market and personal bias could conceivably recreate the era of segregation, albeit as a smaller niche market. The upside seems to be 0 and the downside seems to be quite grim, so why would we even consider the question of returning policy back to the way it was during Jim Crow as if it worked so well back then.