While we are pro-adoption as a forum, we are also well aware that by far not everybody has got access to a good rescue. We are also all too much aware that there are huge differences in standard of care between rescues. In the English speaking world anybody can call themselves a rescue without any licensing and welfare supervision; the same as with breeders. The results can be accordingly (with some rescues being places that need rescuing from themselves) and they cover indeed any shade in between.
That is the reason why we have got a list of vetted good standard UK rescues on this forum and refer to Guinea Lynx for US and Canadian rescues. I also know most decent Australian and Kiwi rescues that operate to a comparable high standard.
While adoption is great, welfare is as important an aspect. If somebody wants to get a second-hand piggy from the free-ads, especially in an area where access to a good rescue that offers boar dating under expert supervision is not an option, then they are also doing a good deed that should not be poopooed on on principle.
Spayed sows are generally rare but they do occasionally turn up, and they are most definitely an option to consider for a single boar!
What we are doing in those cases is pointing out the potential hidden issues and helping to work out ways to ensure that the poster can minimise the inherent risks with taking on companions on spec from an unknown background. Piggies end up on free-ads for all sorts of reasons; we should never generalise a priori but rather do research into the background before discounting a valid opportunity.
PS: One of the reasons why we have survived as a forum when so many have failed is that we don't clobber people over the head with a one message agenda like far too many other online places but because we explore with them all their possible pesonal and local options with their various pros and cons and their possible ways of making these options work for them on a cery practical basis. This will hopefully allow them to make their own informed decisions, whichever that is. Welfare is a goal that is not achieved by shouting it from the rooftops but by working on it in a thousand little practical ways.
A lot of pet store pets aren't cared for properly and are sometimes sick when you buy them. Many rescues and shelters offer neutered or spayed pets that have already been vaccinated too. They also have a wide range of different breeds and animals, all for a cheaper price than buying. 
