Your exact same argument could be made for murder, for sex crimes, for hate crimes, etc. Just because some people might occasionally want to commit these acts, does not make them okay, because they hurt people.
Open relationships already exist. There is no limit on what kind of relationship you can define with your partner, so there is absolutely no “necessity of lying and cheating”. That is just an excuse for people who don’t give a shit about hurting people.
Maybe I misunderstood it then, it seemed like they were presenting this as a defence for people who cheat, like “don’t blame them, blame the society which ultimately causes it”.
Edit: reading again, it very clearly says “… Instead of vilifying it [infidelity]…” So they really are trying to say “stop getting upset about it”