Does viewing pornography count as a sin, given that it leads to an increase in its availability to others, in light of Allah's saying: "That they may bear their burdens in full on the Day of Resurrection, and some of the burdens of those whom they misguided without knowledge. Unquestionably, evil is that which they bear"?

If you have repented from watching pornography, regretted it, and are determined not to return to it, you will not bear the sin of those who watched it because "the one who repents from a sin is like one who has no sin," as stated in the Almighty's saying: "Except for those who repent, believe, and do righteous deeds; for them Allah will change their evil deeds into good ones. And Allah is ever Forgiving, Most Merciful" (Qur'an 25:70), and His saying: "But indeed, I am a Perpetual Forgiver of whoever repents and believes and does righteousness and then continues to be guided" (Qur'an 20:82), and His saying: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" (Qur'an 39:53).

As for one who has not repented, he bears the burden of those he caused to fall into disobedience, because he was a caller to misguidance, in accordance with the Almighty's saying: "That they may bear their own burdens in full on the Day of Resurrection and some of the burdens of those whom they misguide without knowledge. Unquestionably, evil is that which they bear" (Qur'an 16:25), and the saying of the Prophet, peace and blessings be upon him: "Whoever calls to misguidance will have a burden of sin like the sins of those who follow him, without that diminishing anything from their sins."

And Allah knows best.