Oh, you can get pretty close. What you do is you look at their attitudes towards the marginalized individuals, to marginalized communities, their opinions as a whole, their advocacy, their friendship groups, etc.
If, on balance, they appear to support and promote people of colour or transgender people (as much as they do any other people group) - then this person is probably not racist or transphobic.
However, that's haaarrrd. And doing that groundwork doesn't win you clicks as a media outlet. Whipping up a mob does win you clicks however. And advertising revenue.
And then many people - who have only read those articles - shout about it, like mobs tend to do, it seems like it has universal approval, and people assume it's probably true.
If you don't define words like "racist" and "transphobic" to be solely about intent, those words become meaningless.