Not always true.
1 - PornTube and other sites cost money for premium content. Some men also pay for online video sex sessions with cam-models.
2 - You can if your hands are not clean or contain bacteria. You can give yourself a urinary tract infection or nonspecific urethritis.
3 - People get ripped off at home all the time by clicking on malicious porn links, internet scams, email romance scams, phishing attacks, etc. Some people are also coerced into sending large sums of money to cam-models as gifts. People also occasionally get attacked by home intruders.
4 - Depends on how you define cheating. Some people may feel violated, deceived or cheated on if their partner is discovered having online video sex sessions, either with a prerecorded video, or by paying for a private sex show with a live cam-model and/or paying a cam-model to provide special custom videos upon request.