If the sale of debt is targeted towards someone vulnerable, as your dying of thirst in the desert example is, then that is immoral. However, the entire system that allows anyone to go into debt is not immoral, and it is generally not targeted. As long as there is no lying and obfuscation, you reap the consequences you make.

You should no more expect someone not to collect debt than you should expect to walk out of Walmart with whatever you want. If someone needs charity, that should be supplied OUTSIDE the normal system (non-profits, governments, friends and family), otherwise the system itself is ripe for abuse.