"Most transwomen are lovely and no danger to anyone
This frankly isn't true - from the goals and methods of the trans movement we can see that most men who call themselves 'transwomen' are, at worst, terrifying misogynists or, at best, indifferent to women's safety and humanity if it gets in the way of their wants. That's not 'lovely' - why should women sugarcoat this behaviour and lie on their behalf?
I would say that the most important thing in putting forward an effective argument against gender identity ideology is to not use the framing and language of trans activists.
Unfortunately, too many feminists reflexively adopt this language and framing, either because they haven't thought about it deeply, or because they believe that signalling submissiveness via use of the 'correct' language or disclaimers ('most transwomen are lovely!') will make people more receptive to their arguments. Because a woman using plain language and asserting firm boundaries will be seen as aggressive, impolite, unfeminine. When in fact using plain language and drawing firm boundaries are the only way to cut through the cognitive distortions and doublethink that rule in this debate.
So, for instance, don't talk about 'women and transwomen'. Talk instead about sex and gender identity - how they aren't the same thing, and we still need laws and language to recognise the reality of sex. Never use the word 'transwomen' at all - its a meaningless category that just confuses people, given that a 'transwoman' is literally any man who identifies as such. Most people think it means 'transsexual' and they also have this bizarre idea that feminine-presenting men are extremely vulnerable and oppressed, and therefore not only no danger to women, but in more danger than women. It isn't true, but that's what people think when they hear the word 'transwoman'. Most people will prioritise these supposedly super-vulnerable men over women, so don't use this word, or you will have lost the argument already.
Instead, use language that makes clear what is actually being pushed, eg., 'men who ID as women', 'male individuals', or just men. This reminds everyone of the reality of sexed bodies and why we need sex-specific spaces and services in the first place.
Don't go on the back foot when TRAs storm in and accuse you of hatred, bigotry and literally killing people - just point out that this is hyperbole and untrue, that you believe in everyone's humanity, but that sex is a material reality that needs to be accounted for in law and policy. Keep pointing out that sex and gender aren't the same thing and that 'gender' means 'sex roles'. Ask why they are trying to promote sex-role stereotypes ('gender') as the basis for what men and women and boys and girls are.
Note that plain, firm language does not have to equal being snarky or angry. Of course it's only natural to be angry at what's happening, and perfectly reasonable for women to be snarky to men (and women) who are promoting such grotesque sexism, but calm arguments do tend to win the day. My point is that it's possible to be calm and polite WITHOUT giving ground on language or women's rights.
Joan McAlpine is a fantastic role model for this. I am so impressed by not only her calmness in the face of TRA attack, but the clarity of her language and the way she reframes the debate. She keeps bringing it back to the simple point that sex and gender identity are two different things that must not be conflated. It's really worth studying her twitter threads and seeing how she cuts through the spurious arguments and emotional blackmail with calm, clear language and facts. Notice also that not once does she use the term 'transwomen'. She sticks exclusively to the language of sex, which is what makes her arguments so clear and persuasive.
Eg. twitter.com/joanmcalpine/status/1101251118611525633?lang=en
twitter.com/JoanMcAlpine/status/1105945838218592264
twitter.com/JoanMcAlpine/status/1109015164064591872