Are all the people who are loving and supportive on social media to people who are thinking about transitioning really loving and supporting?

Yes they want people trapped in the wrong body to escape that body and find happiness.
No, they aren't supporting of people who don't think transitioning will make people happy.
Yes, they defend the rights of people who want to transition by shouting down bad people.
No, they aren't supportive to people who change their minds and want to detransition

Who are the oppressors?

The people who oppose the escape of unfortunate people who are trapped in the wrong body.
The people who prevent people from speaking out against transitioning with loud noise.
The people who are violent to those who believe there are only two sexes

What are reasons to believe that people who say that transitioning made them happy might not be telling the truth?

A lot of people commit suicide after transitioning.
A Swedish study showed that many still had mental issues after transitioning.
Surgery does not cure delusional thinking.
Happiness depends on accepting who you are – not on trying to force others to pretend that you are what you really aren't. 

What is wrong with biological males competing in women's sports?

They sometimes cause serious injuries to the women
The estrogen they take gives them bigger muscles.
There's nothing wrong, they help their teams win
They have an unfair advantage over biological women.
Women are uncomfortable being in locker rooms with them.