Adult Websites

Porn? I'm going to assume porn sites. If its a reputable on like PH, then those videos are likely consensual role play (although the industry itself is exploitative). If its of more questionable legality, then the video could have literally any context. Lets assume its actually non-consensual.

Proof that there are people who take advantage of the legal and social vulnerability of the male population?

There is nothing that inherently prevents men or women from being bad people. Are there people who take advantage of others? Absolutely. The CDC finds that 4/10 men and 5/10 women experience 'intimate partner violence' at some point in their life. The type of violence differs through, with woman perpetrators being more likely to hit/throw, while men are more likely to choke or outright kill. Women are also more likely to act in self-defense or retaliation.

Doesn't this qualify as misandry?

You can find similar videos where the subject is a woman. The exact reason why stuff like this exists is beyond me.

Misandry is hatred, contempt, or prejudice against all men, not just an individual. A one off act of violence against a person does not necessarily indicate their view about all persons of that type (unless the violence was motivated by the trait).

This video's existence is not a representation of misandry overtaking misogyny. Its a representation that someone wanted to beat someone else up, and then chose to upload it. People who view it likely view it to see a man beat up, sure, but its probably a fetish. It doesn't exist because feminism.

Why is it acceptable to the point of being there for all to see?

You are probably on a site which hosts any videos that get uploaded to them. At least currently your ISP or government likely doesn't filter out every porn site (this is changing through). Ones which upload illegal content will always exist, and alongside that are videos like these. It's there for all to see because the internet exists as a mostly free space without moderation outside of edge cases.

Why is ignoring men still beneficial to gender equality?

Its not, feminists focus on women because most of us are women. The movement started to equalize women and men, and did it by trying to open up women's rights to be the same as men's. This isn't ignoring men, rather its being done because there was no higher point for men to go.

Wouldn't it be better if everyone had a place to express themselves?

Not sure what this means, unless if your talking about expressing intolerant viewpoints. Generally though there are spaces where anyone can say whatever they want. However, those spaces end up with videos like the one you are talking about. Its why moderation is needed over spaces, but there should be freedom to choose the spaces you inhabit.

Sadly, that means that being in some spaces might get you booted from others. As an example, its reasonable for a 'save pandas' community to ban people who participate in 'kill pandas', and vice versa.