We are woefully uneducated about even the concept of mental health.
I don't know of any therapist that doesn't have a specialty and figuring it out is required before you get licensed by the state (CA) simply due to the different licenses available.
There's an undeniable undercurrent of racism if the goal is for the therapist to be a blank white slate for their client, but you misunderstand the goal. The goal, in being a blank slate, is for the client to be comfortable expressing themselves. The therapist, as a professional, is working on behalf of their client and can't let personal opinions that conflict with the client's beliefs come to bear, except in the most exceptional of cases when someone is in imminent danger.
If the client is scared, to the point of not being able to bring it up, that their therapist will judge them and yell at them and verbally abuse them, therapy won't work. If I hate 'lesswrong' and think its stupid, but yet my therapist has built their online presence and career on it (as SSC has), merely knowing my therapist's beliefs on the matter will pollute any response I could have. A good professional therapist can detach their personal opinion of 'lesswrong' from the client's need to rant, and the theraputic value in helping the client figure out their underlying feelings and possible trauma, and to NOT engage with the concept itself. Thus, by not knowing a therapists personal views on every possible thing they might tweet about, this is achievable. If not achievable, then at the very least, worth striving for, for the client's sake. The therapist's goal is to heal the client. The therapist's opinion on misc topics is irrelevant to healing the client.
Is it reasonable? Therapists go to school for years and practice for hundreds of hours, to pursuit of that goal. Some are more successful than others, and still, falling in love and transference - by therapist or client, is simply an occupation hazard.
HOWEVER. This is not the same as saying the therapist needs to not be a human being, otherwise we might as well have therapy by texting an AI (Note to VCs: I know it's stupidly tempting, now's not the time, GPT-3 and ML models a therapist do not make). It's incredibly important, on a personal level, that you find a therapist who specializes in the kind of work you need to do on yourself, in a compatible way, and has some level of similar lived experience.
If I have to explain what the word "woke" means to my therapist wile I'm working through racism in my personal life, that's just not going to work. If I have to explain to my therapist, why being asked to touch my hair, or being told "smile, it makes you prettier", is rage-inducing, it's really just not going to work.
Find a therapist that's like you - in looks, and gender identity+orientation because therapy needs that commonality to serve the client well, but also recognize that's easier said than done.