> In any event, Salafis do not constitute a majority of Sunni Muslims (by far),
True, but they have a lot of influence. I'm not Muslim, but my uncle (by marriage) is. My uncle has never really been the mosque-going type, but his father was. I remember his father complaining that the Salafis had taken over his mosque, using all their Saudi money. And I don't think his experience was particularly atypical.
Also, I don't think this is unique to Salafism. [0] repeats basically the same point of view (contraception is permissible to delay having children, but not to prevent it entirely). That's not a Salafi website, that's a website aligned with the Muslim Brotherhood – the Brotherhood are not Salafi, they represent an Islamism which is more traditional in its scholarship than the Salafis are
[0] https://fiqh.islamonline.net/en/contraception-permissible/
> and Sunni Islam is not a religious system that includes a clergy.
Whether that's true depends on how you define "clergy". Sunni imams or ulama are just as much "clergy" as Jewish Rabbis or Baptist ministers are. The claim that Sunni Islam lacks "clergy" relies on defining "clergy" in a narrow sense inspired by Roman Catholicism, Eastern Orthodoxy and "high church" Protestantism, and ignoring the broader sense in which the term also gets applied to Judaism and "low church" Protestantism, among others.
> and people who identify as "Salafi" do not automatically or necessarily adhere to rulings in the way you seem to imagine
I'm Catholic–how many Catholics do you think follow the Catholic Church's teaching that most forms of contraception are prohibited? So I was never making the assumption you are assuming I'm making
> The original issue was whether getting married and having kids is obligatory for Muslims, a requirement of their religion like ritual prayer, fasting during Ramadan, etc
In a strict sense, you are right – all Sunni ulama agree that marriage and children are mustaḥabb (recommended/encouraged) not fard (obligatory). However, I think it is more complex than that for two reasons (a) in some Muslim subcultures, certain things which are officially just recommended/encouraged become de facto obligatory, not necessarily due to the letter of religious teachings, but due to social pressures which exist in those religious communities; (b) something which is only mustaḥabb in the general case can become fard in specific cases, and certainly you will find ulama who think that sometimes happens in the matter under discussion, and if the specific cases become broad enough, they can end up outweighing the general case in practice