"Trying to ban things won't work. Just look at murder. Murder is illegal, yet it still happens! Therefore, let's legalize it."
This logic might sound good, but you're really comparing apples and sheep here.
The simple fact of the matter is, it's actually quite hard for one person to kill another. Those that can are usually in compromised mental states or psychologically unsound and for those that aren't, killings are fairly obvious affairs that are not easily covered up. Plus, murder has a directly harmed victim.
Pornography, on the other hand, does not require such mental compromise or exceptional circumstances or unusual individuals to participate in. Especially now, with the internet, requires very little in the way of visible effort to participate in and, finally, there is no
directly harmed victim, at least, not in a way that is obviously and consistently clear.
This is why the comparison is so flawed in that there are two highly different things needed to accomplish a "ban" on each thing. Banning murder is easy, and taps into already existing policing and cultural norms regarding usurping vengeance, kinship vengeance, and cycles of revenge. Banning porn, especially in the US, has not such preexisting systems or cultural norms to tap into. From a enforcement side of things, the infrastructure required to implement an effective ban on porn would involve massive amounts of monitoring of and interference in the Internet to a degree I don't think ANYONE should be comfortable with, as any system like that once in place would be easily expanded to involve the policing of OTHER things those in power find
undesirable, like, say, political opinions or news stories they want spiked.
This then gets into the serious question: would the benefits of banning porn, including an effective enforcement system (which would be required as otherwise banning porn becomes a meaningless platitude), be worth the cost? Given how censor happy many people are in regards to political ideologies and other matters, I would say no, no it would not be. Any system effectively put in place to ban porn would be easily subverted to ban other things online.
And don't trot out that society HAD effective porn bans in the past. Firstly, no, there's not been an effective porn ban since humanity discovered how to DRAW, you will find examples of pornographic images even in things like Middle Age illuminated manuscripts, and the printing press only expanded the market for such things (Penny Dreadfuls, etc.). Secondly, while there were legal porn bans they were not very effective AND they also depended greatly on social stigmatization: the shame of purchasing or being seen in public with such paraphernalia. This is no longer a dependable effect. Between the massive growth of home delivery and easy ordering and, of course, the internet, one cannot reliably know if a person decides to look at porn... unless one is willing to exercise considerable violations of personal privacy by monitoring their browsing history and making it public.
So... it's nice that you want to ban porn, but have you really thought about how much power you're giving the government if you do so? Do you really TRUST it with that power, to never go beyond porn, to never try and weaponize it against other things that the bureaucratic elites find distasteful or problematic?