The question is, did someone tweet something racist??
Because if they didn't, but you're putting out and signing a letter saying you are distancing yourself from violent racists, without giving examples, then you are fomenting hate and violence of your own, and yes, painting a target on someone's back.
As KJK pointed out, that is exactly what happened to her in Australia.
If I write a letter calling out and condemning the paedophile ring who run my local bowling club, hundreds sign it and it gets national attention, what do you think the people will think? That I'm a jealous shit stirrer or that the local bowling club is running a paedophile ring?