The problem with diagnostic labels such as ADHD is the science behind them is rather weak. For example, [1] concludes that the distinction between ASD, ADHD and OCD is not biologically valid–in other words, it is not an accurate distinction in terms of what is actually going on in the brain. (And that's just one paper, I can share plenty more that reach similar conclusions.)
No denying that many people have found diagnostic labels to be very helpful in practice. Gatekeepers make services/support/treatment dependent on receiving a diagnosis (or even a particular diagnosis – some labels get you more help than others – in particular, ASD generally gets much more resources than ADHD, creating pressures for people with ADHD to be diagnosed as having ASD as well in order to get better services [2]) However, they shouldn't do that – people should get services based on their actual need (severity of symptoms, level of dysfunction, etc) not on whether and which diagnostic labels they've been assigned. Limiting services based on diagnostic labels is actually discrimination by diagnosis [3], and surely we can all agree that discrimination is wrong?
Anyway, the fact that people get these kinds of benefits from diagnosis is a social/cultural/political fact, not a scientific one. It is a set of facts about the configuration of mental health systems, insurance systems, education systems, government disability funding, etc – and all those facts are ultimately rooted in policy decisions, and policy is determined by politics, and politics is part of culture. Some critics argue that the entire DSM-5 diagnostic system as a whole is more a product of society/culture/politics than of actual science [4].
[1] https://www.nature.com/articles/s41398-019-0631-2
[2] https://www.smh.com.au/lifestyle/health-and-wellness/the-phr...
[3] https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1440-1754....
[4] https://cepuk.org/wp-content/uploads/2014/03/Diagnostic-syst...