I'm married, and my husband and I had sex before we married. I think that it's a personal decision that one shouldn't take lightly, if anything. But, marriage for many, is merely a piece of paper while to others, it's a sacred bond that should last forever. For some, sex is a means of strictly seeking pleasure with another person, but to others, it serves as a physical and emotional bond. It varies from person to person. I can see your points, OP - but, when emotions and chemistry are involved, sometimes our best theories on life get moved aside.
It can also vary even in the same person. I unabashedly seek casual sex, it's my primary method of getting laid right now while I'm doing my MS and PhD. I haven't been in a serious relationship for a while and have had no time or desire to.
Yet I know what it's like to have deeply emotional, connected sex with a romantically loved partner: it's a different thing, and something I look forward to again when I meet the right person. Sex doesn't have to be one or the other, and I know that isn't what you were saying, this is more just for readers in general.