As a person of Christian faith willing to share my faith, I'm not sure I "target" vulnerable people. I don't discriminate for who receives my sharing. I'm spoiled to live in a society and social circle that doesn't have a lot of suffering. Even when people pass away, those still living are often rational and emotionally mature enough to understand that their grief is temporary, and that they can move on with life after grieving. We should support them in the manner that they'd find most helpful, and it's not complicated. In fact, if me sharing at that moment would cause them to seethe with hate, I probably should back off; they should be able to feel love from me, not hate, and if they feel hate, I'm doing it wrong.
Correspondingly, I'd need to go out of my way to share with vulnerable people, like to a homeless shelter or an orphanage or the like, as I don't run into many vulnerable people in everyday life. I am sure you would have no issue with my volunteering and donations. You'd only have issue with my sharing my thoughts to these vulnerable people. But again, I'm not targeting them, and I'm not discriminating towards them. I say the same things to people who are mature, successful, and solid. My faith just happens to power my actions, and my actions hopefully reflect my faith. As written in James ch2 v18: "But someone will say, “You have faith; I have deeds.” Show me your faith without deeds, and I will show you my faith by my deeds."
If I run into a vulnerable person and my sharing helps them, that's great. That's happened before. If I run into a nonvulnerable person and my sharing helps them, that's also great. That's also happened before. If either of them want to reject me, I feel sad about it, but I imagine it's similar to how a nutritionist feels sad when someone refuses to eat healthy food. If they reject me or my sharing, not much I can do about that, and everyone makes their own decisions. If they don't agree with my decisions, well, despite believing in the Judeo-Christian God, I am not God to make them think the way I want them to think.
I am not sure how to live out my faith and volunteer without sharing what drives my actions. You may find that in poor taste because you do not agree with my faith. But it is not sensible to do some action and at the same time reject or suppress the reason why I perform that action. I posit that it's simply a coincidence that my faith delivers a message that can appeal to vulnerable people. You find it to be malicious and disingenuous. I find it to be logical, as this is what Jesus' sermon on the mount was all about. Blessed are the poor, the weak, the meek, etc.
I'll concede that there are people of faith who seem to care about getting the message out while forgetting what the message actually means. I'm sorry those people exist. But I hope you'll be willing to consider it's not supposed to be like that. The above quoted James ch2 v18 is what it's supposed to look like.