Hello, Navi and Gustavo,
Like Gustavo, I think all four sentences sound bad, Navi. This thread reminded me of a historical one, which I was finally able to locate. All the coloring and much of the other special formatting was destroyed, naturally, in the change of platform, but the thread is here.
In that thread, the fun finding was that purpose infinitives tend to work fairly well with passive clauses when the passive clauses concern "institutional" actions, as opposed to personal actions -- viz., my example "Traffic lights were installed to alleviate traffic congestion."
In this thread, Navi, you seem to be taking things too far. Not only are you not using institutional actions, but you are trying to omit the object in two of the sentences, almost as if you could piggyback off the grammar of "Our truck was too unreliable to use in a bank robbery."
That kind of degree-related comparative construction deals in adjectives, not in passive constructions. If you are holding in reserve an example where the passive clearly works with an omitted object in the infinitival, now would be a good time to unveil it. For now, I'll just say that I liked Gustavo's revisions. I also like these:
1/2) Our truck was stolen for use in a bank robbery.
3/4) They were kidnapped and exploited as slaves.
Regarding "institutional" actions and shared subject, consider this:
5) They were drafted to assist in the war efforts.