No doubt that bitcoin had been accepted long time ago as a payment method,that's the reason of it's creation to serve as an online payment option that doesn't require the involvement of an intermediary to execute payment.Exactly,the porn industry can't be left behind as other industries have been accepting Bitcoin and other cryptocurrencies as a method of receiving payments.
I would add to this argument. There are a few industries where people would like to hide their identity and porn websites are the ones where people would like to visit and pay anonymously. The other industry is the gambling and crypto payments give a boost to this industry too. The people who are still using credit card on porn sites are either not aware of crypto or there is something wrong in their approach
Of course, your argument has a strong point that is right on track to a key psychological driver for cryptocurrency adoption. You may call it privacy in sensitive transactions and there you will think of making payments with cryptocurrencies.
While these porn and gambling industries got benefited from this crypto adoption but on the other hand some people argue that crypto is supporting wrong things like helping the porn and destroying the society. Well this argument may be valid but still we cannot blame crypto alone, porn was there when there was no crypto. We need to focus on exploring the broader implications