In order to be sexually objectified wouldn't sexuality need to be dehumanized? Doesn't this really all boil down to the puritan mentality that our very unique human sexuality is somehow shameful, dirty and wrong? Society objectified SEX and successfully removed it from the table as one of our most important and fantastic and unique human qualities. you can only really sexually objectify me if you remove my humanity from the ogle, which of course makes it very hard to self-objectify.
This is really a really interesting point what you say about people's attitudes towards sex being shameful and therefore making is less human. I hadn't thought about this but now you mention it I do agree with this. Thinking back I realise that many people I have known who have been particularly derogatory are people who seem to have a disconnect between sex and what is socially "appropriate". So their female friends would be treated as humans, but any woman they thought was hot or might have sex with was suddenly a "slut". Nameless, worth only their body and a high five from their male friends. I wonder if some of this behaviour came from being raised to believe sex was wrong, as it might explain why someone would lump all shameful and disgusting behaviour into one area, because to them it's all as bad as each other.
I can't remember where I read this but somewhere recently I read an article which talked about rape and puritan views. It explained that if you are a puritan Christian, your punishment for multiple actions around sex is going to hell, therefore rape is no more punishable and would be lumped in with everything else. Which could be why some people believe women who "sin" by having sex or doing porn, shouldn't then complain if they then get attacked, even if they get attacked in a completely different circumstance.
I do think that to be sexually objectifying you would be dehumanising the person. It's part of the definition that you are degrading that person to object status, and therefore in this situation their humanity wouldn't matter.
I guess if you were staring at someone, it is objectifying if you look at a person, you know you are making them uncomfortable but you do not care and continue because you find them physically attractive. It is pretty human nature to care about what other people think and feel, so to disregard the other persons thoughts and feelings because you are getting sexual thrills would be dehuminising/sexually objectifying them. Kind of like watching an animal in a zoo, people don't care if the animal is uncomfortable with being watched. While you could stare at someone finding them attractive, but when they notice you, you look away to not make them uncomfortable, you are acknowledging that they are a person with feelings. Physical sexual attraction does not necessarily mean sexual objectification. I personally only think it gets to objectification (in a real life social situation sense) when you care as much about that person as you do meat on your plate. And I do think people who get to that point regularly probably have something missing in them and how they see others. It is not natural or normal for humans to be that desensitised when interacting with one another. There is a reason social media exists, we're curious as hell about one another.
I also agree with
@Mollie_ that I don't think a moment of judging someone on their looks when you meet them is objectifying. Again, definition, you aren't seeing them as an object. You are just acknowledging the instant information you have available. Lots about someone's looks can tell you about a person, their skin tone, eye brightness, if they choose to wear make up, if they groom themselves, how healthy or clean their hair looks, how they choose to dress. You can even tell things about that particular day. Then expressions and body language tell you a lot about a person, their mood and what they are saying to you. Bear in mind that while we are one of the few animals who primarily use sound to communicate, we still do communicate a lot with our bodies (which most people don't consciously bother to read or have no practice so cannot read). Sexual attraction might be a part of your initial assessment of looks, if they have a pleasing face you may decide you would like to spend more time with them, or be more willing to trust them.
I don't think any of this is objectifying. If you consciously put them in a scale of one to ten then yes that is objectifying (and you may have issues with your own self esteem), but that is a completely different story from meeting someone and judging their appearance. I don't know what you've read, but that sounds like an misinterpretation of data.