The problem isn't any one person.
The problem isn't even just Mermaids.
The problem is a movement that suggests we have some mysterious indefinable 'gender identity'.
The problem is an unevidenced ideology that relies on undefined terms and arcane theory.
That suggests we must accept 'gender identity' as an article of faith.
That sets up the idea of 'trans' children.
That encourages the breaking down of boundaries.
That says 'queering' is unquestioningly a good thing.
That repeats hyperbolic statements about suicidal ideation.
That asks children to decide what 'gender' they are when even adults in academic gender studies courses are unable to clearly define it.
That then suggests that the child's 'gender' must be 'affirmed' and threatens any adult questioning or disagreement as 'conversion'.
That celebrates dysphoria as part of an invented 'trans identity'.
That creates a movement with flags, codes, in-groups and narratives such as the 'glitter family' or 'rainbow family'.
That casts outsiders as transphobic, bigoted, pearl-clutchers, 'haters', homophobes, etc.
That encourages a culture of secrecy, between schools and families, between children and families, between charity staff and the public.
To me personally, that whole movement looks like something that I'm not allowed to state clearly on here. I'll let you make up your own mind.