You have raised some very valid questions here Tari. And I suppose there are varying degrees of MBS!
I am sure most of have our limits and know what they are. I for one, will never have a cockatoo or a Macaw for different reasons. I will never have a cockatoo because I KNOW I couldnt give them the attention that they would need and still keep my other babies happy. And I will never have a Macaw because I am afraid of their beak
Then there are different reasons why people take on a new bird. Maybe they do it for the love of the new bird, well obviously this must be a factor to some degree else why would you take the bird;) ? But there are other reasons. Maybe its because our Greys are one person birds and another member of the family wants a relationship like that with a bird. That was the case in my family for 2 of my birds.
Birds did not evolve to need human interaction, therefore some birds do better without it. I have small birds who are very happy little guys but who do not need, or want handling by me. I give them toys, I give them food and water and I let them play with each other. I don't consider that these little guys are suffering for want of my giant hand in their face on a daily basis! But most of all I gave them playmates of their own kind.
I know for sure that there are individuals out there who get birds just to say they have bird X or Bird Y. But I honestly dont believe that those types of people are on a site like this one. Those kinds of people are probably not interested in enriching their birds lives, and in looking for help to interact with them. So why would they be reading a forum like this?
I consider the members of this forum to be the elite in bird owners for the most part. And I truly believe that if a bird is plucking, or biting, or whatever, that our members, with the support from the rest of us, have the best possible chance of improving that birds quality of life.
However.... having said all that.... each and every time someone considers taking in another bird, they should definitely reflect on the questions you raise regarding vet bills, space and whether they need interaction, and whether you can give it!