What you're criticizing isn't someone making a major life decision based on feedback from internet strangers. Its a person who has made a major life decision reflecting and joking about the experience in a space assumed to be for trans people trying to deal with (via jokes and memes) the overwhelming hatred they've dealt with.
A) this is clearly a stupid meme post that IN THE MEME itself indicates the person is no longer 16 (in fact if you look at post history they're now at college so > 18).
B) was responded to with a meme in an of itself. The idea of an LGBTQ+ pipeline is well known to LGBTQ+ people. Yes they'll make fun of it in response to a meme post. In ACTUAL discussion, they will earnestly discuss that transitioning isn't for everyone; don't stop because of other people, but also if you're not comfortable or transitioning isn't make you happy, you learned something about yourself (you might not be trans).
But to put a fine point on it: Telling children that they have options for self-expression besides the default gender binary isn't child-grooming. Full stop. And in marginalized communities, you may only have internet strangers to deal with (if your family/friends or local community have no safe spaces). Obviously, for such a large decision you should be working with a therapist (if there's a non-transphobic therapist in your area AND you can afford it/its available) to work through this rather than internet strangers; and that is OFTEN discussed. No one is under the impression that these are small decisions. They're just demanding that they be understood as VALID decisions.
But to boil down a trans-support group (with your 'I call it how I see it'/'won't somebody think of the children' type bullshit) as 'castrating young people' means that you're not as logical / unbiased as you think you are, you clearly DON'T know what you're talking about, AND, as the OP stated, you are transphobic.