The OPs argument is that it's not illegal to develop or sell the software but it might be to use it. Nice get out...
It's also not illegal to sell marijuana seeds as long as you don't grow them into plants. Thanks for that but what the hell else are you going to do with them???
Same goes for software developers like this, they may act all innocent and blue eyed by developing the software but they know for a fact this the tool will be used by someone to breach copyright or privacy guidelines which makes the promotion and development of such tools immoral and unethical in my view.
It's a difficult issue that is faced by a lot of tool or service providers, i.e. do you provide a tool or a service knowing that that tool or service could be used in both an ethical way and in ways that are not ethical.
The supply of most types of tools or services require some modicum of soul searching, as there are ethical grey areas with a lot of things...
Do you provide
web hosting, knowing that some of your customers could use their websites to breach other people's copyright, or use their web hosting mailing account to spam people?
Do you run a
business forum, knowing that some of your members might make copy and paste posts, or link/embed images, which infringe the copyright of others?
You could try your best to monitor the above and crack down on it after it has happened, but there is still the risk that providing the service, you are helping it to happen in the first place.
Do you provide
ecommerce software, knowing that some of your customers could take it away and use it to sell dodgy goods or goods that infringe copyright? If it is software which is taken away, then you have little control over its use thereafter.
I personally have made such soul searching decisions too in the areas of hosting and providing ecommerce websites (although not takeaway ecommerce software websites yet), and as for business forums, copyright infringement was one of the (many) reasons I never ventured into that area of running my own forum.