This is inspired by the webchat yesterday with Stella Creasy and Caroline Nokes where 'be kind' was used.
I don't think 'be kind' works well when you are talking about groups of people. Being kind requires knowledge of what another person wants or needs, and also has connotations of 'helpful' 'doing a favour' or 'allowing someone something to which they are not absolutely entitled'. It works best on a one-to-one level.
For example, it might be 'kind' in one situation to speak loudly as the person you are talking to can't hear very well. In another situation it would be kinder to speak quietly because someone is very sensitive to noise.
You could not therefore say 'it is kind to speak louder' because sometimes it is and sometimes it isn't.
Therefore a simple 'be kind' doesn't work without knowing who is being asked to be kind to who.
It doesn't work in a conflict of rights situation because being kind to one person is not being kind to another. It also requires clear acknowledgement of what behaviour is 'kind' (going above and beyond what is necessary) and what is simply 'right' (giving someone what they are entitled to).
If someone points out that a Muslim women would not want to share a changing room with a transwoman, 'be kind' gets us precisely nowhere, because being kind to one is not being kind to the other.
'Being kind' implies that there is also a time and a place where not being kind is OK. 'It would be kind of you to share those sweets with your brother' implies that there are other times when sharing would not be required.
What we are generally discussing is a situation where (generally women) are bing told to 'be kind' to transwomen but the recipient of the kindness feels that it is their right, not a favour.
I really don't know why any politician would think it is a solution to a genuine societal problem. Deaf people wouldn't want politicians to say 'please, television companies, be kind to deaf people and subtitle your programs'. Noone wants to rely on kindness.