I think you are both over-simplifying. In neither case - secular liberals, or Christian “zionists” - is there a singular set of motives (indeed, I agree than in the US at least, the majority of secular liberals support Israel’s right to exist as a nation).
In the case of Christian “zionists”, while the classification itself suggests that they support Israel, they do not do so for monolithic reasons - some have millenial concerns just like you say (the so-called “dispensationalists”); others support Israel because of a more emotional connection to the ancient Biblical tales; others, because they feel that belief in those biblical tales implies belief in zionism; still others (and possibly a majority), for reasons somewhat similar to those of secular liberals who support Israel.
Now, I’m not a Christian American (far from it), but I do know a few. There is no need to straw-man their position, and claim that they all support Israel because of millenial concerns - that simply is not true. It is akin to those who claim that all “secular liberals” hate Israel - which is also not true. There are definitely some Christian zionists who support Israel because of the role Jews are supposed to play in millenial fantasy, and there are some secular liberals who hate Israel. Neither is the majority view - though it is very popular for people on either side of the cultural divide in the US to attribute either ‘dispensationalism’ or ‘hatred of Israel’ to their opponents – as this very thread attests.
Understanding the Evangelical Christian's Support for Israel | Opinion!