It should be noted that there is no selection of students for the field of study at the university (apart from a high school diploma) and AFAIK there also is none for the course.
The university may not apply a formal selection process, but there are always selection effects going on. High schools encourage some students more than others, parents decide whether they're going to support their children in higher ed, couples decide whether they can afford to have one person studying full-time... all of those, and countless other factors, play a part in selecting who does and doesn't show up in your class on Day One, and who completes the course and the degree.
In places where overt discrimination is illegal or socially unacceptable, this kind of "soft pressure" is very important in understanding things like how your class ended up 80% male.
These main reasons why I find this offensive/disrespectful:
The students were viewed and addressed primarily through the lense of group membership, and not as individuals.
Forget about gender for a moment, and suppose you're a doctor studying lung cancer. You notice that within a certain population, 10% of people who smoke regularly get lung cancer, and only 1% of those who don't smoke get lung cancer, even after controlling for other factors that might affect cancer rates.
It is impossible to point at any single case of lung cancer and say for certain that it was caused by smoking, because even non-smokers get cancer occasionally and any given person is exposed to thousands of factors that might affect their cancer risk. But in a large population, when ten thousand smokers get lung cancer, we can be pretty sure that nine thousand of those cases were caused by smoking.
So it is with issues of gender bias. It is very hard to point to any one person, any one decision, and say with certainty that this one decision came down to gender bias. But looking at the group level provides quantitative evidence that many decisions are affected by such bias - even if we can never identify exactly which ones.
If you're aware of instances where the issue could be addressed at the individual level, by all means do so and/or let your professor know, as appropriate. But given that this is the start of term, it sounds as if they're trying to prevent such behaviour before it starts.
Replacing "male" with any other group makes the statements offensive or absurd.
If you change words to different words with different meaning and different history, then yes, just about any sentence can be made absurd.
Your class is over 80% male. Most areas of STEM are historically male-dominated, with quantitative evidence of subtle but important biases against women. (Sometimes not so subtle! Whether or not one agrees with your professor's approach, it is very much influenced by that context; if you change "male" for some group that hasn't dominated STEM and your specific class to such an extent, then of course the statement becomes ridiculous.
(Just because I know somebody's gonna bring it up if I don't address it: yes, there are a few professional fields like teaching or nursing which skew heavily female... and those fields do acknowledge this as a problem, and are trying to improve that balance.)
While the instructions to not look down on/patronize female students are correct, they are (in my view) indirect accusations of sexism.
Well, yeah. Chances are very high that there are some sexist people in your class, and it sounds as if your professor is trying to address that. Unless somebody is able to provide her with a list of who is and isn't sexist, I'm not sure how they could do that without the message also being heard by people who aren't sexist. If you're certain that you're not one of those people, then don't take it personally.
When I did first-year chemistry, our instructors warned us not to mouth-pipette dangerous chemicals. They were not accusing me, Geoffrey B, of being silly enough to take a mouthful of hydrochloric acid. But they didn't know who the silly ones were, so they had to warn the entire class.
The contents of the talk, which took 5-10 minutes, were not related to the lecture and thus were a waste of time for students. The issue might be important, but I was there to learn different contents.
Every class has a certain amount of admin content. Professors will talk about how your assignments are to be graded, safety rules for prac classes, what to expect from exams, etc. etc. None of that is "what you're there to learn", per se, but it's important to the learning process. Whether the professor handled this effectively, I can't really gauge without hearing the full version, but it doesn't seem unreasonable to give a few minutes to something that's important to ~ 20% of the class and may affect their ability to learn.
Is my view justified? Is such behavior acceptable for a professor? Should I let the professor know the way I feel?
As you may have gathered, my take on this is different to yours. But let's assume that I haven't persuaded you to my way of thinking, and you still think her approach is wrong...
IME, when you want to change somebody's behaviour, the most effective approach - where possible - is to understand why they're doing what they're doing (what is the problem they think they're solving?) and then to offer them an alternate way of achieving that goal.
In this case, it's pretty clear that your professor is concerned about possible discrimination against women in your class. One way or another, they are going to act on that concern. If you don't like the way they're currently handling it, then you need to offer some other way of handling it. If you don't want them addressing the whole class on this, what alternative are you suggesting?
(I would strongly recommend doing a fair bit of background reading on these issues first. There's been a lot of research done into things like selection and retention of women in STEM, and it's quite likely that they're familiar with that research. If you want to offer workable solutions, you need to be familiar with it too.)
Otherwise... I can tell you for nothing, they already know that quite a few guys feel the same way you do about what she's saying, and they've decided to say it anyway. Unless you have alternatives to offer, it's unlikely that arguing it with them will shift their position, because you won't be telling them anything new.