Others have already addressed it while I slept, but I don't know that anyone did it with the bluntness and simplicity you require, and one key element was missed.
Firstly, as
@BigJake pointed out, everyone knows men don't catcall to get sex. I mean, there may be some complete psycho who takes women's general responses of a)completely ignoring it, b)calling him a sleaze/slime/other name under her breath, c)tensing and walking away as fast as possible, d)telling him outright that she doesn't like it as positive reciprocation, but...well, you don't appreciate sarcasm so I'll stop there.
So, why do they do it? The need for sexual validation, particularly validation of their masculinity, which they do be demonstrating their power over women in public space by harassing them. You literally just made my point, that catcalling is about aggression and power dynamics, for me. The very point which you denied.
Onto, how do they "obtain" what they want? Well, let's start by not treating other people like objects that need obtaining and intimacy like a reward and an entitlement. Here is where you completely missed the point of the bank robber analogy and why I called your post "rapey." Men are no more entitled to women's bodies -- and this extends to harassing women -- than is the bank robber entitled to that money. Your post implied that harassment can be considered a reasonable method of "obtain[ing]" a woman's body, and that is absolutely loathsome.
Now, "rape" is a big word. And not one I'm going to throw around lightly. When I say your post had a "rapey" tone, I
mean it. Consider that. That is how
you sound. It doesn't mean you sound like a rapist, but it does mean you sound like someone who has normalized and internalized the idea that sex is something men are entitled to.
It tends to happen that when hoist up my petticoats and step on my Catcalling Soapbox people accuse me of making mountain of a molehill, or else say that I'm too sensitive and see every attention from a man as an affront. But women know the difference between looks and leers (No one can really help looks. I give looks! Looks can be pretty great!), and as
@{ Emilia } has already said, context matters (there are times and places to pick up a chick, and I tend to make it pretty obvious when I want interact and when I do not). As for why catcalling is such an important issue, well, let's look at a typical day:
Dozens of catcalls, from the moment I step out my door at 7am to the moment I get home. This is with headphones on and "shields up" as I call it (I often blank out male attention as much as possible because of the amount of harassment I receive, to the point where I apologize in advance to male friends and colleagues in case I blank them on the street), so these are just the super loud, physical, and aggressive ones. Imagine how you would feel if people commented on your body
all day long. What if you weren't feeling very good about yourself that day? What if you were already feeling self-conscious? What if you'd just had nightmares about the sexual assault you experienced as a child? -- Let's remember the percentage of women who've experienced sexual assault. What if you were just having one of those days where you really didn't feel up to dealing with people, but you gotta go to work, and you're a woman, so you know that on the street your body is fair game. That's just the way it is.
What if you were actually feeling your best? Maybe after hearing, "God bless you baby," "Give us a smile!" "Look at those pink cheeks, I see you blushin'!" "Mmmm, why don't you walk that sweet pussy over here?" "Oh, sexy, sexy! Damn, must be a fuckin' lesbian," "Hey mami! Hey, mami! Hey, I'm talking to you! I'm talking to you, you fucking bitch! Fucking ugly fucking dog bitch!" for 12 hours you might not feel so great anymore?
Now, add to this the fact that behind all that noise, you always know that one of them might actually hurt you if you don't react the way they want you to. Oh, and, you don't know how they want you to react, either! Fun, huh?! You know this because it's happened. Not a lot, but enough to know that it's always a possibility.
Starting small: There was the group who always got me by the autoshop on Montrose and it was raining, and I just couldn't handle the feeling of their eyes on my face that day, so I pulled my umbrella down low to shield my face. One of them snatched it out of my hands.
Then there was the guy who slapped my ass on the sidewalk.
Then there was the guy in line at the bodega, old enough to be my father, who told me I was sexy so I ignored him. He said, "Come on, sexy, don't ignore me," and started stroking my face. I slapped his hand away and he grabbed my wrist. The bodega owner threw him out before it went further.
Then there was the group of guys who wouldn't let me leave the train station and I had to wait with the station agent until the police came.
Then there was the guy who got up in my face while I was talking on the phone with my mom, licked his lips and said, "Mmmm sexy, What you got on under that coat" -- it was about 12ºF and I was wearing a parka that literally went from my neck to my ankles because, guess what, it doesn't matter what you're wearing! -- his intrusion put a hitch in my conversation and after he was, at least so I thought, out of earshot, I told my mom "Sorry, some gross guy was catcalling me." He heard me, came back, grabbed me by the shoulder and started yelling in my face, calling me "bitch" and all that. Middle of the afternoon in Astor Place. It only lasted a few seconds, thankfully.
Then there was the guy in the park off Delancey street, whose advances I tried to ignore, and he responded by grabbing me by both wrists and shaking me.
Then there was the group of guys who were catcalling me when I was 17, and I told them to fuck off, and one grabbed my by my braid and tried to pull me into an alley and I had to pull a boxcutter on him.
Then there was the guy who sat next to me on the train and whispered in my ear, "When you get off I'm going to follow you home and rape you."
So, imagine what it's like to step outside every day, and know that, while most men are great and don't harass women, a good portion of them do, and will harass you that day. And while most of the harassers are just trying to "obtain external sexual validation," a handful might just come after you if you don't give them the sense of power they crave. Then imagine coming online, and seeing someone try to justify their behavior, like YOU ARE DOING. Then imagine trying to enjoy a movie or TV show, and seeing the culture that supports their behavior reinforced over and over and over ad nauseam.
So, let's think through that logically. How should feminists address these issues if not by trying to put an end to hyper-sexualization of women in the media, decontextualized objectification in the media, normalized harassment in the streets, and the notion that women's bodies are something men are entitled to and can obtain?