The link is that sex (even gay/lesbian etc sex) is not a sin, what people like sexually is not the business of their employeer, and if we can accept people doing parades for the right to fuck each other in the ass or similar, we sure should be able to accept people reading the word "porn" on a website at work.

That's the implicit link. The explicit link is that LGBT advocates and activists have frequently defended porn and freedom of sexual expression through it, too.