A good question – one that brings attention to two Jewish values that must be balanced – a question worthy of this time of year, when we are encouraged to ask questions. :-)
You don’t say anything about the stream of Judaism in which you (now) practice, but in any case it sounds as if you are finding one of the areas where there may be different opinions to be had even within a particular stream. For example, in a more stringent, halachic (Jewish legal) community, there can be several concerns that may underlie a reluctance to invite someone who is not Jewish to a seder (or a meal on a holiday or a Shabbat).
One may be a concern with inviting a non-Jew to a holiday or Sabbath meal, because one will be cooking for that meal. The idea is that the leniency of allowing one to cook in advance of (or on) the holiday by using the concept of an Eruv Tavshilin (the partial cooking ahead of time, only completing the process on the holiday), for example, should not be used to prepare food for someone who is not obligated to observe the holiday and is not themselves restricted from cooking. Since you are only supposed to make as much as you will need – no more – making extra for a non-Jewish guest is problematic. This restriction is a large part of why some people will not invite a non-Jew to join them for a meal on a holiday (and all the more so, on Shabbat, when all cooking is prohibited).
Another argument that may be advanced is that one should not have a non-Jew, someone who is not obliged to observe the holiday, join you to do so. At various times and places in Jewish history, this restriction had to do with protecting oneself, for example, from informers in the wake of the Inquisition. In other times and places, it was simply that you were including them in the ritual of the seder, which is directed to be held with those in your household, where only the members of your household are to eat of the offering; only if your family is too small to consume the entire offering are you to join with another household (in the same situation) in order to finish the entire offering. (Shemot/Exodus 12). From this, the understanding is taken that only those in your household, and by extension, those who are part of Am Yisra’el, are to be included in the ritual – so non-Jews would be excluded.
I would guess that in a community where Halachah is followed, these restrictions would be brought to bear to support not inviting a non-Jew to a seder, and there may be more reasons.
At the same time, even in these more halachically oriented communities, there would be a tendency towards the acceptance of a non-Jew at the seder for other reasons.
The restriction on cooking may be put aside if, for example, it is to save a life. I suspect it could be argued that if a starving person were to appear at the door at the time of the seder, it would be legitimate to claim that one must allow him in and feed him to preserve his life; in that case the concept of pikuach nefesh might trump the halachic restriction on cooking for a non-Jew on a holiday. A variation on this might be if the prince or king of a state appeared and demanded that they be invited to the seder and to eat to prove that nothing evil or nefarious was going on, and to disobey or disregard such an order might lead to persecution and even the death of Jews. In this case, it seems to me, that it would likely be appropriate to include them and even to cook for them.
To invite non-Jews to the seder has been discussed and approved, at least in some instances, in Mishna Berurah 512 6 (Commentary on Orach Chayim by the Chofetz Chayim). More, there is an argument that could be offered that the limitation on inviting a non-Jew to a ritual act (the seder) should not apply, as the seder is not itself the ritual or cultic act; it is an educational re-telling/explaining of the story (the mitzvah is to tell), and so anyone could be invited because it is not the actual ritual in itself.
So even in an observant, halachic community, there are a variety of responses, depending on the circumstances, and I would venture to say that practices vary from place to place.
In the Reform stream (about which I am writing), the idea of inclusion is much stronger, with greater emphasis on outreach to and education of non-Jews, as well as Jews. In addition, given the common practices among many Reform Jews regarding a very relaxed view concerning application of Kashrut (dietary restrictions) and the understanding that halachah (Jewish law) is generally not binding on them today (while the ethical – or prophetic - precepts concerning social justice and treatment of others are generally to be followed in full), the concerns noted above are not particularly relevant in the mind of many in the Reform movement - so inviting a non-Jew would not be a difficult choice to make.
Adding to that, with the current rate of intermarriage (at least in the USA) exceeding 50% in many locales, the frequent blending of families, and the free mixing and socializing of Jews and non-Jews today, there are many families that contain both Jewish and non-Jewish members; to hold that only the Jewish members of a family could participate in a family seder seems counter-intuitive, at best.
For most Reform Jews, there seems no reason to hold that we are to exclude anyone from attending a seder, and they, too, can point to the concepts you ask about in your question: if we are to remember and treat the stranger as we would ourselves, how can we legitimately exclude them from our sedarim (plural of seder)?
In sum then, the Reform answer would tend to be that one can invite non-Jews to attend, and even participate in, the seder.
Rabbi Joe Blair
Answered by: Rabbi Joseph Blair