Anytime I hear someone say they can't afford to pts an animal, I say you can't afford to have an animal if you can't afford the medical bills.
Which brings me to the issue that medical costs for 5 equines could get really high.
Yes. People try to give me horses all the time. I have taken a couple free horses and could have had dozens more over the years.
People also offer me low cost pasture boarding, so I can have more horses. People I know look for lower cost boarding so they can put a horse or two out to pasture and have more horses.
What limits me personally is that I know horses don't stay in a static state. You can buy a healthy horse, even a young one, and they can have a major injury, sever a tendon or something and require expensive vet care. They can get Lyme disease, Cushing's, Laminitis, PSSM. They can lose all their teeth and need an expensive soaked diet.
A friend of mine wants me to put my mare "out to pasture" on her farm so I can afford another riding horse. My mare is 29 with Cushing's. I need to watch her closely for white line disease and infections so I can catch them early. I need to make sure she takes her Prascend every day. I need to soak her pelleted vitamins so she doesn't get choke since her teeth are not good. If she begins losing weight, I will need to adjust her diet as she ages more.
A person might think a young horse will not have problems, but although there is less risk, there are no guarantees. I personally won't take on more horses than I can care for if they become injured or ill. A person might think they could sell the horse to a good home if their finances changed, but an injured young horse is no more sellable than an old horse. Especially if the condition is permanent. And it's not always a good decision to put down a young horse with a permanent issue. Sometimes they can't be ridden but still are pain free and having a good life. Or they need expensive shoeing that keeps them sound, but makes them difficult to find a home for.
My opinion is that we can all do our part by taking the best care we can of the horses we have. If everyone did that, there would not be a kill buyer problem. At some point in your life, you will probably be ready for a new horse, as I have been at times, and then you can take on a needy horse with all their expenses and feel great about it.
That doesn't mean we should feel like we ought to save all the needy horses we see. If you looked around your own community, you could probably find a new one every day.
Many well meaning people "rescue" horses that end up needing to be rescued from them. Taking on more horses than you can care for and then being unable to give them the best care might be a worse feeling than knowing you can't help all the others out there. These ones are your responsibility, after all.