I'm sure for most people rehoming is a huge and very difficult decision. No matter what the reason (whether you agree with it or not), the individual or family feels they can no longer keep their baby. If this is the case then their baby is better off with another family, they are unable to offer their pet what's needed. At least they're taking the time to find a good home rather than taking their baby to a shelter or pound or God forbid abandoning it in some field. I would not judge too harshly, you can't know the whole circumstance.
If you're referring to people who just casually get a pet and decide they no longer want it, then again the pet is better off with someone else. (Although I think in most situations this is not the case, especially on this web site
)