Evolving's narrow biological sense doesn't involve purpose, is most of the iffy bit, heh. It's just noise thrown against a wall with some parts sticking and some not. There's nothing to trust, just stuff to adjust to (or die).
And I don't think it's a matter of deserve, exactly. There's precious few on this planet that'll outright say, or believe, that the elderly (or much of anyone, really, barring maybe some nebulous bad people grouping) deserve to starve to death in a pile of their own filth as they fritter away whatever material goods or safety they may have accumulated due to their mind aging into a stew of incapable mush.
Stuff like pensions are more an acknowledgement that a people are just kinda' fucking bad at the planning and logistics involved with making that not happen, especially in edge cases where family is incapable or unwilling to provide and/or the increasingly non-edge case where the old person lives way longer than expected (for lack of a better word). Damnably often not nearly a sufficient one, but... it's not something I'd categorize as a profound distrust. Just an attempt to paper over a persistent problem. Distrust is probably pretty close to it as a descriptor, but there's nothing profound (or major, or whatever) about it. S'just kinda' routine.
It's not just pensions, mind. Every sort of elderly assistance/retirement program is basically the same thing, with varying levels of effectiveness. Folks aren't going to be able to provide for themselves forever, and someone's gonna' have to (or eventually deal with a corpsemess, I guess).