Are those who simply work, mind their own affairs and forgo social functions perceived negatively at work?

Yes. I do this and Im sure I am perceived negatively.
People don't understand that some come to work, not to make 'best friends' who will soon turn on them, then spread their business all over the office.
No thanks

Yep, I honestly hate socializing at work. I get they want to build "team spirit" but it's a job, not a get together with friends. Less fake friends, less drama

Yeah it is. They are also the ones who are the happiest as they avoid the office drama.

It depends on the workplace. If you work with a bunch of socialites they don't tend to understand non-socialites.

It definitely depends on where you work. I usually didn’t want to socialize with my co-workers, we rarely had anything in common and it seemed like a recipe for unnecessary drama. But when I accidentally befriended someone in upper management who’d once been a musician, it ended up fast-tracking my career and I got promoted.
The adage about it being “who you know” is not totally wrong.

It depends. If the social function is on the clock, then typically yes. Most people I know don't fraternize outside of the office. But if we have a team lunch or team event somewhere it's generally expected that people try to attend. If there is critical work to be done it's generally acceptable to skip. But if no deadlines and always skipping it isn't viewed well.