Negotiate the business requirement and make the scoping decision

As a product manager and a business analyst, you are going to
present the suggested scope to your development. Do you see
this is a "negotiation" process? Do you see that typically the
product management wants to get the items IN and the
development tries to get the scope OUT? Do you see that you
ever need to ADD MORE into the scope so you can GET MORE
after the "negotiation"?

I do not have a clear answer for all the above questions, but I
can see that these are two models, two types of assumptions,
and two different processes:

1. People playing different roles sometimes need to play the
devil's advocate. The best decision is reached via the process
of negotiation among the people representing different interests.
In the software requirement scoping case, the product manager
represents the "requirement" side, or the "demand" side, and
the development represents the "delivery" and the "supply"
side. The assumption is that we cannot avoid people having
different interests. Instead of trying to solve the conflict of
interests within one's mind, disputing, debating, discussing,
negotiating, and finally reaching an agreement is the way to go.

2. Defining the scope can follow the standard decision making
process and can be scientifically done. The assumption is that
there is really no conflict of interests. Both product management
and development are toward to the same goal - delivering the
right solution timely to satisfy the targeted customers. Making
profit for your organization in a short run as a mean to maximize
the shareholder's value in a long run. The customer satisfaction,
effort, time to market, risk of delivery, avoiding rework, and
quantity should all be considered. They can be considered in a
systematic way as an individual or a team effort. A product
manager who propose the scope should consider both side or
even more factors as mentioned above. The reasoning and
the justifications are discussed with the development for
ensuring the completeness of proposal.

I do not have an answer. I can see both models explain the real
world situation. What do you think?