Actually, both the Tali romance and the Garrus romance bother me. According to the fiction present in the game, the tissue of a Quarian or a Turian is toxic to humans and Asari (and vice versa). Consider the romances with that in mind.
In Tali's romance, not only is the mere act of breaching the suit likely to make her incredibly ill but she is doing it in order to conduct an exchange of fluids with an entity comprised of poison. The mere act of kissing one another would guarantee some amount of toxic tissue was exchanged, and the act of intercourse itself would (if you assume intercourse with a Quarian is more or less identical to intercourse with a human female) deposit an enormous load of toxic tissue. Thus, not only is Shepard risking his own health in the process, he is asking Tali to breach her suit thus placing her in danger and then going through with an activity that will, as an inevitable result, result in some quantity of poison being delivered to her. The conclusion here is virtually inescapable: Shepard obviously does not care for Tali and his reckless disregard for her safety tells me he probably just wanted to nail another alien like some sort of future douchebag bro.
In the case of Garrus, recall that you are outright told (if you ask) that significant lubricants would be necessary to avoid intense discomfort during intercourse. Beyond that, the Turian body structure has numerous bony protrusions throughout. Given the delicate nature of the tissue in the female genital area (delicate enough that tearing is relatively common even when having intercourse with a member of the same species who, for the record, tend to keep our bones inside our skin and under layers of fat and muscle), it would seem inevitable that significant trauma would occur to the Female Shepard during an act of intercourse. Considering that, once again, Turian tissue is toxic, this means that she was basically injecting poison into her body through various tears in her vagina.
Neither of these encounters shows anything resembling sound judgment but at least FemShep isn't placing Garrus' life in terrible danger, or at least not to the same extent as the Male Shepard/Tali example. By contrast, the relationship possibilities with the human cast and Liara are at least sensible in most respects given that these relationships offer the possibility of reproduction (if desired) and do not involve intentionally introducing toxins into each others bodies by default.