I don't think they are mocking Christianity. Remember, many Christians celebrate Valentine's Day, as well.
To me, Valentine's Day is a celebration of love and caring. Perhaps, similarly to Christmas, it has becom way too capitalistic. Anything to make a buck!
However, if I spend a dime and take the time to say "I love you", it is quite difficult for me to classify that as a mockery of Christianity.
Just an opinion.
Love you All and Happy Valentine's day,