One of the most common questions Rabbis tend to get is about contraception. Specifically a discussion about family planning, and how long one can use contraception for. Before the man has fulfilled his mitzvah of Peru Urvu to avoid doing a Mitzvah Dioressah could be problematic. However, once they have a boy and a girl there is now a mitzvah drbanan of lsheves.
My question is why do Rabbis say this is a question that must be asked, I don’t ask a Rabbi if I should have guests over for Shabbos. What is the difference they are both avoding doing a biblical commandment (one is Hachnosas Orchaim the other peru urvu). I don’t ask my Rabbi if there is a ‘heter’ to avoid visiting my parents for a year to avoid Kivud Av? Why by family planning is there such an emphasis on asking the Rabbi when other mitzvos (which are not time bound) there is no emphasis to ask?
The answer I am looking for should be based on sources why lsheves/pru urvu is more stringent than other Yoreh Deah cases.
Based on the comments this has been added: Since birth control until more recently was highly problematic, from a Halachic standpoint, there was never any questions about using it, unless Pikuach Nefesh it was Assur. In the past few years where the actual BC is not an issue itself, there has been little public talk in terms of Halcahic writings on it. We are left to infer from the writings which we will call the source. This source can be the Rambam as answered by Dov. We don’t paskan by the Rambam if the SA does not concur with the ruling. We have a Gemora as RabbiKaii and Dov wrote. (Besides the Ramchal in his letters disagreeing with this concept) The Shulchan Aruch does not bring this as his opinion.
We are left with the Shulchan Aruch which says if someone remarries he should remarry to a woman who can have children even if has been Yotze peru urevu. We see from this that he is pro having more children if he can. The minhag has always been to ask questions like this to our Rabbis, I shall continue to do so.
I am still hoping someone will be able to help find a source that can help me understand the Halchic (NOT HASHKAFIK) reason why to ask whether one can take a break after being Yotze Pru urvu (+1) when timed mitzvos generally we don’t ask (for example I don’t know anyone who asked a rov how much money they should put away a month for writing or buying a sefer Torah)