There are some who use the "feminism" banner to promoted sexism towards men. I've seen posts that talk about wishing for a world where no men exist etc and it gets praised under the guise of feminism.

Imo that isn't feminism, that's just misandry. If you swapped our the word "men" with "women" in those posts, they would rightly be called sexist.

I am definitely a feminist in that i believe in equality and believe that women have had a number of challenges presented to them that men typically dont experience.

I also, however, believe there are challenges that men experience that typically women dont.

Feminism is equal rights and opportunities for everyone. My added thing is equal responsibilities. This is the dictionary type of definition.

Most people (at least the vocal ones) are either completely sexist (both sides - feminazis and sexist men) or think it is only about promoting interests of women.

I can’t give you all the possible views off the top of my head but I'll try.

1. If you are not a feminist, you are sexist. - There is no nuance or leniency for human nature. This makes skeptics jump to opposition because they feel attacked for their behaviour. Any further push only makes them more apprehensive.
2. Men have it so good - This is kind of a mixed bag for even me because it is situation and topic specific. Men have had better opportunities for some things like education or jobs, yes. But they have fared worse in some other things like emotions, expectations, dating, etc. Now, if someone who struggles with a lot of things is told "Men have it so much better", they will not agree because any one person can only experience their own problems. On the other hand, there are men who feel women have it too easy with how they can earn money by selling porn, they can get out of situations by crying, how easy it is for women to get laid, etc. I don’t necessarily agree with everything but this is what I have seen people say. So, this makes "Men have it better" laughable for some people.
3. Where are the equal responsibilities? - Feminism promotes equal rights but (conveniently) ignore the equal responsibilities part. A lot of women like to be damsels in distress and also want to enjoy the perks of freedom and equality. This is something I personally despise a lot.

It is. Most people associate feminism with promoting women and not equality. Most people don’t look up the definition in a dictionary

People are unique and everyone has varying opinions on every topic, so how can they be simplified to a simple yes or no. There is a spectrum for everything. People who are at extremes find it easy to fit in yes or no categories but everyone else feels lost.

For example, there can be a guy in a rural area who supports his family's women by letting them go to school/college, working, dating who they want but he is very adamant that they should not dress and wear makeup like "whores". Would you call him a feminist? Why or why not?

it's probably good for social shame to be introduced for sexism, fascism, racism, etc

Yikes, this is a hard no. People don’t change their views like this. Also, you are being a bully if you shame people for anything. Just because you think you have a moral high ground does not make it okay to impose it on others. You are no different than religious evangelicals if you do.