BENEFITS
of a marriage? Ironically, you people are asking THE BENEFITS of a
marriage when in actual fact, a marriage brings NOTHING but merely
a recognition of
the next phrase the couples' love has evolved, in
which the ultimate quality of sacrifice makes much better sense and
worth than in BGR, which has it's limit during test date phrase -
the couple sacrifice much more, in all dimensions, in a marriage
than BGR.
Tell you the truth, you can't see those so called 'benefits'
because you are using different yardsticks to measure those
intangibles. You are trying to equate the goodness of marriage via
material/dollars sense, which completely makes no sense. The same
way anyone could have tell you that love is completely redundant
because even without it, technically speaking, you could still
survive, breathe and live. Worst still, you could get hurt very
badly, so why get involved at all?
Own the world, but loses its soul? 
Generally, there are three forms of marriage (sometimes, a mixture
of two or even three):
Cirumstances:
Forced by circumstances, a marriage happens without much choices.
People generally marry because of reasons other than Love. Shot-gun
marriage, eyeing on fortune, etc.
Biological/Chronological:
People get married because it's the time to get married. Gently
pushed by biological clock, people plan and get married when they
feel that 'it's time' - whatever it means to them. Sometimes people
get married because they are together 'too long' and felt that they
needed to induce something to revive the stagnant love.
Spiritual:
People get married because they want to spend the rest of their
life together. Simple and truthful.
The following contrast you have shown above, merely
shows the alternatives a couple could have without the marriage
commitment. But then again, it makes no sense to
have something just for the SAKE of having. One good example is the
babies example you quoted. Obviously, people can adopt - however,
for people who truely love little ones, there is a VAST world of
difference between their OWN child and adopted ones, especially
since they could conceive naturally. What about house? Anyone can
own a house - it's WHO you are living with that makes the
difference. You can stay in any house of your dream...alone and you
will feel worst than one staying in a 3-room flat with love and
laughter.
What you are
trying to do is measuring the intangibles through tangibles
means, which I stress again, makes zero
sense.
I don't blame you because you are not there yet. And
because you have yet to reach that level, you are highly subjected
to people who THOUGHT they are there, but sadly, nowhere near
actually. These 'people' impart their negativity to you and you
accepted their mindsets. Then again, but makes you think their view
is the true meaning it holds?
P.S (Astro): Certain people's horoscope birthchart are more
resilient to marriage (Esp. Saturn in 7th house). A powerful Uranus
transition cum progression can trigger a divorce BUT that has to be
promised by your birth chart in the first place. Some people do not
have divorce aspects in their charts, instead, their charts shown a
need to learn the areas of love and relationship through alot of
cosmic learning. Through freewill, they might temporary break up or
whatsoever, but the bonds never seemed to sever completely.

Cheers