Cass uses the term "toxic"/ "toxicity" three times in the report. She says that a variety of polarised positions (on the correct form of health care for trans people) are unsupported by evidence, and that the resulting toxicity made her job much more difficult, and also creates a negative environment for the people who need the healthcare. She doesn't use the expression "both sides".
She says:
Despite the best intentions of everyone with a stake in this complex issue, the toxicity of the debate is exceptional. I have faced criticism for engaging with groups and individuals who take a social justice approach and advocate for gender affirmation, and have equally been criticised for involving groups and individuals who urge more caution. The knowledge and expertise of experienced clinicians who have reached different conclusions about the best approach to care are sometimes dismissed and invalidated.
And
Yet from the start, the Review stepped into an arena where there were strong and widely divergent opinions unsupported by adequate evidence. The surrounding noise and increasingly toxic, ideological and polarised public debate has made the work of the Review significantly harder and does nothing to serve the children and young people who may already be subject to significant minority stress.
And
There are polarised debates about a range of societal issues involving transgender people in the UK, ranging from use of single sex spaces to participation in sports. Although these issues are outside the scope of this Review, they have an impact on gender-questioning young people because of the inflexibility of the factional opinion and resulting toxicity of the debates. Services for children and young people have evolved within the context of this broader picture and every person involved in this work has been and continues to be affected by the dialogue
I am going to assume that she knows what she's talking about, and that she's being quite nuanced. She's not interested in who started it. She's concerned with the effect it is having on the children she sees as her responsibility. She is not on "our side" or "their side". She has her own side, which as a doctor she should. She's commenting on the crossfire.