I don't want my cashier to have the final say in whether I get emergency contraception, or a pregnancy.
If the Obama Administration requires EC be sold over the counter to those 15 and over, requiring an ID check by the cashier, then the anti-choice crowd will push to give cashiers the same "rights" they gave pharmacists. The "right" to interfere in a persons private decisions regard the use of their uterus. Pharmacists can simply say "I don't believe in EC" and leave a cis woman or trans man or any other person for whom the possibility to get pregnant exists frantic to find another pharmacy in which to purchase the EC, while the clock is ticking.
I am sure the anti-choice crowd are already brewing up legislation that would allow a cashier to refuse to ring up a pack of EC, claiming it's compromising their morals by "participating in abortion" (even though EC isn't abortion).
This might allow the expansion of "conscience clauses" to cashiers to deny to ring up not just EC, but refuse to sell nail polish, or caffeinated beverages, or cigarettes, or any other number of products, to a cis woman or trans man they even suspect may be pregnant. I don't want a cashier to have that much power. That isn't protecting the cashiers right to religion. That is giving the cashier a right to force their beliefs onto me. That is an invasion of my religion or lack thereof.