What is good and what is bad?
What is good or bad is highly subjective, and people have opinions that are all over the board, unless one has a set of standards revealed by God. We normally refer to those as God's Laws.
Having sex only within marriage has many obvious and quantifiable social and personal benefits. I could not even begin to list them all. Sex out of wedlock can lead to adultery, broken families, and divorces. Although that is not always the case, the fact that it is sometimes the case is very problematic for individuals and for society. Many social problems could be prevented if sex was restricted to marriage.
86% of women who have abortions are unmarried women and that tells us the abortion rate would be much lower if nobody had sex out of wedlock.
TABLE 1. Percentage distribution of U.S. women obtaining abortions
Relationship status
Married 14.3
Cohabiting, not married 31.0
Never-married, not cohabiting 45.9
Previously married, not cohabiting 8.8
https://www.guttmacher.org/sites/default/files/report_downloads/us-abortion-patients-table1.pdf
So what are the benefits of having sex out of wedlock?