Against :
Here we have 21 countries which support the same-sex marriage

But what we observe is just the tip of the iceberg. The red countries and inside of the blue ones are those still having laws against homosexual sex.
In general, LGBT persons would experience social rejection

, harassment,

violence

and sometimes prison or even the death sentence like Iran,

where the government described homosexuality as "an illness that should be cured".
Let's me give you an example on the United States
Recent history has brought incredible progress for the US LGBT community in the form of this map

But lesser known is this map over here –

where things get tricky.
"Right now the state of Michigan does not include sexual orientation and gender identity
in its law"

Which means that in Michigan, right now, local businesses are free to refuse service or employment to the LGBT community. And Michigan isn't the only place this sort of discrimination is happening.
So, the question is. Is it legal to discriminate against gay people in the United States?
The awnser is YES.

The fact is, in most states, it's still currently legal to fire LGBTQ people, kick them out
of business that serves the public.

Often as a boss picking another job application
without explanation.
All of LBGT-ers were deeply in the fear of people that were different from the majority.
Under the Civil Rights of 1964, federal and state laws prohibit this
type of discrimination on the basis of race, color, religion, sex and national origin.
This is called Enumeration.
But sexual orientation and gender identity are not enumerated in up to 29 states in the US.
On top of this, there's systematic discrimination in many schools throughout
the country.
The states in red here have "no promo homo" laws that forbid teachers in public schools from mentioning homosexuality at all.
There are too many kids out there suffering from bullying, rejection simply because of who they are.
