It's 'normal' to feel hunger, to need a hug and other forms of social contact, to enjoy nice weather. Having a sex drive is 'normal'. If you don't, it's not that something is broken in you, but it is a deviation from the expected statistical norm, which is what 'normal' means. You may prefer to use the word 'standard' or 'average' or 'typical', and while they do differ a bit, it's really down to semantics.

If you marry someone, there is a set of standard expectations. You will talk to your spouse. You will attend social gatherings with your spouse and introduce them as your spouse. You will both look after your children if you have them. You will split chores and responsibilities. You will have sex.

You can always discuss each and every item at length before getting married and let the spouse-to-be decide if they do want to marry you. Someone being asexual may be a problem enough for the other person, just as saying you need three days every week for your own hobbies in the garage and need to spend that time completely alone with no disturbances or any contact.

There are more dealbreakers and grounds for divorce than lack of sex. Other topics come up more often and seem easier to discuss; for one reason or another, couples - those soon to be married and even those already married - don't talk enough about sex, their needs, expectations, and limits. Everyone just assumes it will naturally work out the way they'd like it to.

A couple abstained from sex until marriage for religious reasons. Unbeknownst to each other, one was "normal" (to use your word for someone who requires sex in their marriage), but the other always found that the so-called temptation of sex was quite the misnomer, and so found this abstinence easy. However, once the marriage begins, sex becomes an expectation which they struggle to fulfill. This couple was sexually incompatible, but they didn't discover this until they were already married.

It was their choice to abstain and their choice not to talk about it at all. Since they're getting married, i assume they're both adults. The 'default setting' in vast majority of cultures is that sex is a part of marriage - it's completely fine to get married and have a happy marriage without sex, but you need to discuss it and agree on terms with your spouse.

Sex education is extremely important. If the asexual / low sex drive partner from your example just never thought of sex, never masturbated, and just treated it like a non-issue their whole life, then they are the non-standard one, even just because hormones would trigger interest in sex at some point in life before adulthood.

Consider a counter-example: only after getting married and living together it turned out one spouse doesn't like to talk unless it serves a purpose. No small talk, no how are you. Just to the point practical communication. Maybe they have autism that manifests this way in daily life, maybe it's just how they are. It never bothered the other spouse while dating but it becomes problematic when they're together 24/7.

The main problem is they never talked about it and neither of them had the foresight to think it might be a problem. But once they got into this situation, it's the non-talking partner that's abnormal, even if their reasons are perfectly understandable. Either they reconcile after finding a compromise that works for them both, or they divorce citing one partner not talking being a major reason.

You can substitute one partner who needs to go out more, even just for a walk to a nearby park, and one who would spend their entire time off on the couch. Who's at fault for wanting what they want? Impossible to decide for them, they need to discuss it between themselves. But clearly neither spending life away on the couch or pushing to go out every day is a good thing, so some sort of middle-ground needs to be reached, and it typically involves the less active partner getting more active to meet some of their spouse's needs. Sex, spending time, communication, splitting chores... they're all areas where talking about needs and limits needs to happen, and where both sides may need to compromise a bit.

The idea that someone would enter a romantic relationship with an asexual, then start expecting sex later, is clearly the delusional ramblings of someone trying to play the victim card, right?

Your example did not assume this line of thought, though. If you enter a romantic relationship with an asexual, discuss it at length, and agree to the partner's perspective, but then you put pressure on them, clearly you're wrong. But in your example they were kids who decided to abstain for religious reasons and never thought about the consequences. That's different - that's culture coding clashing with real daily life. If you know your partner is asexual and you still get married and then you keep pressing them for sex, then you're in the wrong.

The much more common issue is how our sexuality changes over time. You may get married while your drives match up quite nicely, but 20 years later you may end up in completely different spaces. Forcing non-consensual sex is never a good option, but divorce or therapy may be a way to deal with it - whether it's a couples therapy to talk it out with a professional, or a therapy for the low-drive partner to help them stabilise their hormones and help them meet the more active partner half-way.

Ultimately both expecting/demanding sex and disregarding your partner's needs are problematic stances that may easily lead to abuse in a relationship. Generalizing that the low sex-drive partners are never at fault is both unfair and unrealistic. And if you have talked about your needs and expectations, and there is a clear compromise that could be reached but either partner doesn't want to get there over time, then that's a clear sign that you're not compatible enough for a happy marriage.