Why should God punish the firstborn of another nation that was in Egypt?

Question

The Pasuk describes the victims of the plague of the firstborn as follows:

It came to pass at midnight, and the Lord smote every firstborn in the land of Egypt, from the firstborn of Pharaoh who sits on his throne to the firstborn of the captive who is in the dungeon, and every firstborn animal.
כט. וַיְהִי | בַּחֲצִי הַלַּיְלָה וַיהֹוָה הִכָּה כָל בְּכוֹר בְּאֶרֶץ מִצְרַיִם מִבְּכֹר פַּרְעֹה הַיּשֵׁב עַל כִּסְאוֹ עַד בְּכוֹר הַשְּׁבִי אֲשֶׁר בְּבֵית הַבּוֹר וְכֹל בְּכוֹר בְּהֵמָה:

Rashi commenting on this verse states that foreigners were included in this plague:

"smote every firstborn": Even [a firstborn] of another nation who was in Egypt.
הכה כל בכור: אף של אומה אחרת והוא במצרים

What is the reason for God killing the Foreigner who was visiting Egypt? How is that משפט (justice)?

Answer 1

The next Rashi gives two answers to this question:

שהיו שמחין לאידם של ישראל ועוד שלא יאמרו יראתנו הביאה הפורענו' זו

They were happy with the enslavement of Israel, and also so that they wouldn't be able to say that their god brought these disasters upon Egypt.

Answer 2

It is seems from the Mechilta Rashi is quoting that the two reasons of being happy with Bnei Yisrael's subjection and so as not to think it was their gods extracting revenge on Mitzraim, are not said about the Egyptians in foreign lands or foreigners in Egypt. It is said specifically about the firstborn of the slaves and the maidservants. Whereas the point of the death of the travelers was a special drasha from the word 'kol'.

There is a pirush on the Mechilta called Markeves Hamishna who points out in fact that these reasons don't apply. There was no point for revenge from a visitor, only from a slave. He goes on to explain why it is that they did die. He says that any Egyptian firstborn had to die as he is still an Egyptian even though he is out of the country. He says if they were simply visiting the other countries we wouldn't need a drasha for this, it would be simple. The drasha is telling us that even an Egyptian captive in other country was subject to the Makka. The reason the foreigners, had to die, would have also been simple had they been there to stay. But he has a secondary drasha to include Kushites and Chamites which he says is coming to include temporary travelers, as the lands of these people were close, and travel was common.

What comes out is that according to him there was actually no reason to kill the travelers, but we are dealing with Hashem waging a total war against Egyptian firstborns, and what we have is a drasha to tell us that he did in fact kill them, not a reason why.