The left is quite willing to criticize people’s sexual choices. A fairly large segment of the left criticize people who chose to engage in prostitution, particularly if they are the clients, and perversely I think more critical of unofficial prostitution (e.g. sex in exchange for fancy dinner) than straight-up cash exchanges. Sex in an environment of power inequality is clearly objectionable to the left, as is any expressed or perceived obligation to sex even if voluntarily entered into. Much of the left will criticize anyone who abstains from sex for religious reasons. Sex to cement an exclusive marriage that will endure even when one partner would prefer to end it, traditionally the only acceptable purpose for sex in most cultures, is clearly criticized across the left.
I think it more accurate to say that, rather than being unwilling to criticize people’s sexual choices, the left now criticizes every sexual choice but one: Sex for immediate, mutual, short-term pleasure. Sex within a long-term relationship is acceptable, but only if immediately pleasurable to both parties and only if the relationship would exist without the sex. And anybody who doesn’t have sex for immediate mutual short-term pleasure, is criticized either as a prude or as a neckbearded loser so undesirable that nobody would be pleased to have sex with them.