I agree that being told to expect pain during your first time is traumatising, and being expected to endure pain during sex is horrible. Sexual education should include information about everything that might cause discomfort to the person who is on the receiving end of sexual penetration, and advice on how to prevent it.
Tons of articles and also many people in the comments on this post say that foreplay can prevent pain during penetration - and of course it's true that people with vaginas require sufficient arousal, which leads to lubrication and relaxation of the vagina, in order to have comfortable sex.
However, one of the factors that affect whether the person is able to have comfortable vaginal penetration is the character of their hymenal tissue, which is rarely talked about nowadays because it seems like sometimes even mentioning this anatomical structure is seen as perpetuation of the inaccurate and heteronormative social construct of virginity. So I want to assure you that I do NOT believe in the concept of virginity and I am only talking about human anatomy here.
The hymen, also called the hymenal ring or the vaginal corona, is skin-like tissue that frames the vaginal opening - typically it is a few millimetres behind the vaginal opening itself. The thickness and elasticity of the tissue, and the size and shape of the opening (sometimes multiple openings) are extremely diverse: some hymens are fragile enough to tear during completely non-sexual activities such as exercise, some are stretchy enough to accommodate even penile penetration without tearing. Some people with vaginas are born without any hymenal tissue at all, and on the other end of the spectrum there are hymens that prevent menstrual fluid from leaving the vagina so a surgery is necessary to create a sufficient opening.
Just like tearing any other innervated tissue in our bodies, tearing the hymen might cause significant pain in some people. Thankfully, many people have the kind of hymenal tissue that doesn't hurt when stretched slowly and gradually, for example with tampon use or masturbation. Therefore people with vaginas who want to start having penetrative sex should be encouraged to get used to penetration with one or more fingers before trying to put anything thicker inside their vagina.
I think it's a little problematic that the diversity of genital anatomy and its effects on sex are so often forgotten. People who have comfortable and painless first times tend to say that foreplay and being turned on helped them but the truth is that they also very likely had sufficiently elastic or sufficiently stretched out hymenal tissue as well. And people who experience pain are usually told that they weren't turned on enough or their partner wasn't careful enough (that often is the case I'm not denying that at all), but in some cases, the reason for the pain might have been actual physical tissue stretching or tearing regardless of how much they wanted to have sex or how gentle their partner was, and the pain could have been avoided If only they had been told that the hymen was a thing and there were ways to prepare it for penetration in advance.
That's why we shouldn't just say "your first time shouldn't hurt and if it does, your partner is doing something wrong". We should say "there are several things to ensure that your first time is comfortable, and getting used to penetration beforehand is one of them." This attitude also increases the probability that people notice if they have an atypical hymen (such as the microperforate, septate or cribriform type) before attempting penile penetration, and instead of suffering pain and possibly significant bleeding from tearing the tissue, they can go talk to a doctor instead (sometimes a quick surgery in local anesthesia is enough to solve the problem).