You are right, the line is whether the other party welcomed the advance. A lot of very smart people are not socially mature enough to even guess what will happen. Something worked once so they repeat it, over and over again.
Companies should prohibit all internal fraternizing and fire anyone who is caught breaking the rules.
VCs and anyone involved in hiring should have even stricter guidelines. If you are an investor, relationships with anyone who owns another company should be off limits. If you are involved in the hiring process in any way, once the company you work for is disclosed, any potential relationships with that party should be off limits.
Tech has been singled out due to the current news cycle narrative. Many other industries are extremely hostile; expect to see plenty more stories in the future. The biases may not all be gender, but could be things such as seniority, ethnicity. Nepotism and general corruption is rampant in other areas. This is not a US problem, this is a global.