I guess this question is hard for me, lol.
First of all, I kind of wish we lived in a society where people didn't assume other people's sexes and/or genders. So, no, people shouldn't assume...because maybe I might look one way, but identify another. And it should only be up to the individual person to identify themselves.
But like others have said in the thread, I think that most people just want to be recognised as their identities. If someone identifies as female chances are they want to be recognised as female. If someone is genderqueer they probably don't want people assuming they are either male or female.
I'm a transguy and also identify with male id'd butch. There's a lot of narrative in the trans community about passing and being "stealth." A lot of transguys feel it affirms their maleness to blend in and be assumed as a cisguy, and if they like women then they think it affirms them as men to pass as a straight couple. I don't really feel that way. Because I'm not a cisguy and I'm a queer guy into queer women. Being assumed a cisguy doesn't affirm maleness...my transguyness affirms my maleness...as does my queerness. Being assumed straight wouldn't feel affirming to me either. I guess I'm torn because as much as I have never felt female/woman and never identified as female/woman, I also can't say that I'm a cisguy and at this point I'm actually happy to have been born a transguy and not a cisguy. I want to "pass," but I want to "pass" as a transguy
...somehow recognised as legitimately male without people assuming all the shit that they usual assume when they hear "male." Meaning certain genitalia as well as certain experiences, attitudes amongst other things.
So yeah I want people to assume that I'm a guy in my daily life...but I wish that somehow society recognised different types of guys in a positive way. It also gets more complicated than that when sharing experiences and personal histories.
It kind of reminds me of that transguy recently who volunteered to become the leader of a breastfeeding group. He had borne his own child and was breastfeeding his own child and participating in the breastfeeding group. He had the opportunity to become the leader of the group and suddenly all hell broke lose. The media/society making fun of him and making a circus out of it, other transguys turning their backs on him and asking "why you would want to be the leader of a breastfeeding group when you're a guy," and so on and so forth. But people just generally have trouble seeing him as both a guy and someone capable of giving birth and breastfeeding...who should have the right to lead a group like that as much as anyone else who has the experience of breastfeeding their kid.
So I think that brings up the issues of the complications that arise when you assume anything about a person. Yeah many transguys want people to assume they're guys (as it seems this guy does, too), but what does that mean? Their experiences as certain people with certain experiences, histories, physical capabilities and so on seem to conflict for many people with being read as male.
There's a lot of baggage that comes with assuming someone's sex/gender...and I wish there wasn't. That I could be assumed a guy without people assuming shit about my life, my body, my attitudes towards my body and my experiences.