There are very valid reasons for re-homing animals. I live in a military community so pets do have to be re-homed due to deployments, relocating(overseas), and other issues.
There are also allergies, if Bobby my 7 year old had a bad cat allergy I'd be re-homing mine. Notice I said severe, it would mainly depend on what he reaction was. Not everyone can deal with cat allergies, especially when it is their child that is allergic. Also financial, if can afford food but not vet care(and I'm talking period, not temporarily being short on cash, I've been there) then the cat needs a new home. There are also health issues when the owner is just too sick to take care of their pets or changes in family situation where you won't be able to take care of them properly.
There are bs reasons, my orange tabby doesn't match my new furniture(OK then why did you buy the furniture considering you KNEW you had an orange cat.)
I do have issues with people re-homing pets because they are pregnant, I know there are situations when it requires it, but most of the time there isn't. I have severe issues when it is a planned baby and there is no attempt to work it out the second the stick turns blue they get rid of their pets. I know I would try to make it work but I know some animals don't do babies(and they can be other issues) and there is nothing that could be done. That's how I got my Old English sheep dog Abby, they had 5 kids under 5 and the wife ended up pregnant again so the 4 month old dog had to go, they didn't even try. Even though she was better off with us than she was with them anyways.
I can't say never but I know I'd try hard to not have it happen. There are some times when it is required, in the best interest of the animal or issues that can't be helped. You can't always judge people badly for having to re-home an animal, some people have very valid reasons, some just have BS reasons.
I would re-home over them being PTS but only because I would make sure I found them the best home possible or placed them with a very reputable rescue. I would have to find special homes or rescues for mine anyways due to the leukemia. Mine I know would be ok, but there are some that it just wouldn't work for. I know Maude(

) wouldn't have been able to be re-homed and Paul's dog Molly(

) wouldn't have either.
Taryn