in my opinion porn sites who accepting bitcoin is not good for bitcoin reputation indeed people who watching porn very like to anonymous and bitcoin have it but as far as i know that bitcoin is always associated with bad things such as money laundry or something bad else and also porn sites forbidden for several countries so might be porn sites isn't solutions to makes bitcoin growth
And I think that it is a bad thing to do for Bitcoin. It should be used for charities and spread culture and not for such things as porn. It is already used for drugs and weapon, so now we need something really good in which btc should be involved just to keep balance.
Bitcoin has been associates with black market since it was previously used in huge volumes for illicit activities such as drug trade, money laundering, weapons trafficking and many illicit activities. If pornsites were to accept bitcoin then bitcoin will be seen again by the masses as a black currency because it is used not only in illicit activities but also to pornographic sites.