The minhag of reciting Kiddush in shul on Friday night is subject to much dispute. There are many poskim who strongly support it, while others vehemently oppose it. In this article, I would like to present the arguments for both sides by going back to the original sources.
The Gemara (Pesachim 100b) presents a machlokes as to whether or not Kiddush needs to be made in the presence of a meal (bemakom se’uda). Rav is of the opinion that Kiddush does not need to be said in the presence of a meal, while Shmuel argues that Kiddush must be said bemakom se’uda. The Gemara continues to present stories about many Amoraim who all acted like Shmuel, which led most of the Rishonim to rule like Shmuel that Kiddush must be said bemakom se’uda, and that is also the ruling of the Shulchan Aruch (Orach Chaim 273).
The Gemara asks: according to Shmuel, who requires Kiddush bemakom se’uda, why would the custom in Bavel be to make Kiddush in shul? In Bavel, everyone would go home to make Kiddush and eat their meal, so making Kiddush in shul is pointless—it is not bemakom se’uda! The Gemara explains that according to Shmuel, Kiddush was made for guests who would eat meals provided by the community charity in shul.
Tosafos (ibid.) contends that since we rule like Shmuel, if there is no one eating in shul, the Kiddush would be unnecessary because it is not bemakom se’uda. Moreover, Tosafos goes so far as to prohibit making Kiddush in shul because the berachos would be berachos levatalah! Hence, Tosafos concludes that nowadays Kiddush should not be made in shul, and this is the opinion of many other Rishonim.
The Ran (Pesachim 19b) defends the practice of making Kiddush in shul with a very simple suggestion. He argues that even though the reason for making Kiddush in shul no longer applies, as people rarely eat meals in the shul itself, we still do it. This is because of the fact that the institutions that the Rabanan made stand permanently, even when the reason no longer applies (see Gemara Beitza 5a). The Ran proves this from another part of the Friday night davening: Bircas Me’ein Sheva (nowadays known as Magen Avos), which was recited at a time when Jews would pray in the fields, and it was only said in order to prolong davening for latecomers. Yet, we say it anyway, even though we do not pray in the fields. The reason is because once Bircas Me’ein Sheva was instituted, it continues to stand, even when the reason disappears. Thus, the Ran argues that the same should apply to Kiddush in shul; although the reason for it no longer applies, we should still recite it.
The question now turns to Tosafos: The Ran has a very good proof from Bircas Me’ein Sheva; why does Tosafos disagree? Why would we say the beracha of Me’ein Sheva, but not make Kiddush in shul? Why are they different?
Tosafos might differentiate between these two institutions as follows: Bircas Me’ein Sheva was instituted as a part of davening, and therefore, even when the reason disappeared, the institution still stood. However, making Kiddush in shul was never instituted as an integral part of davening; it was just said in shul for the guests that were present, for the sake of their convenience. It was never an integral part of the tefillah service. Therefore, once the reason no longer applies, it should no longer be said.
To summarize: Making Kiddush in shul on Friday night is a machlokes between Tosafos and the Ran: Tosafos contends that it is a beracha levatalah, while the Ran argues that it is not. Some shuls do make Kiddush in shul, relying on the Ran, while others do not, assuming like Tosafos. Both customs have a basis to rely on.