The act of sex does not change after marriage. A slip of paper saying that you are married does not change the act of sexual intercourse. What makes it immoral on the morning of your wedding and moral in the evening after?
Morality is open to interpretation and it varies from society to society. Most societies (with very few exceptions) accept sex in or out of wedlock as what it is: a natural act.
Things should not be made illegal because they are immoral. Morals are ultimately just beliefs, and vary between people, you may find sex before marriage wrong, but that doesn't mean your neighbour, your coworker, or that kid in front of you at the deli does. If it does no harm, let it be done.
All children deserve to have an example of people who continually love each other, and children's parents are that greatest example. The world needs more love, not more pleasure.
The definition of gender itself is 'the state of being male or female' not the state of being one of the '58 genders', therefore we only have two options for genders, male and female. Since gender is decided at birth because of our biological sex, a man cannot be a woman and vice versa.
Sex, when consensual and safe, is one of the strongest pleasures humans can experience. It is fun, exciting, and intimate. Ignoring religious taboos not based on evidence, such sex is a perfectly acceptable activity.
The argument is that premarital sex is immoral (imperitively, objectively, and absolutely counter to what is right), not whether it was safe, enjoyable, fun, or even beneficial.
ergo-emgo