Mordin is brilliant, selfless, and pragmatic. I don't see anything not to like.
Mordin is selfish, calculating, and rugged. His apoliticism makes him sort of a contributor to quasi-evil causes. I'm getting pretty hungry I need some pizza or something, so I could go into more detail but can't really, but he's the equivalent of the Nazi scientist who wasn't actually a fan or proponent of Nazi ideology, but due to his own programmatic and highly controlled ways of thinking and need for stability, can often become beholden to them.
Constructing the genophage versus implementing the genophage, I mean, ok, rather than a Nazi paralell you could argue he was like Robert Oppenheimer or something, someone who again wasn't political or avidly engaged in certain causes, but through his own desire to escape everything and everyone and turn everything into the language of chemistry and equations, ultimately ended up serving a highly politicized and amoral cause (the atomic bombings of Hiroshima etc)
You could maybe argue it's a tragic character, the person who was just a pure hearted student of science, manipulated by the greater forces, but the reality is I have (and had) at least a few extended familiy members who fit the hapless scientist mold to the bone, and the reality is they were capable of tremendous cruelty in their personal interactions and (contrary to the notion of brilliant scientist, or arguably even as a direct consequence of that notion) great stupidity, and so ultimately I am not inclined to view that as some myth making and not grant them a great deal of leniency.
It's something various societies around the globe tend to worship in varying fashion, the go it alone solitary scientist who has all the answers to all the questions, who is objectively free of tainted politicism, but all those people who prop up that myth really do is plant the seed of destruction, for then it becomes clear that all that isolation from reality and building up their own personal hero myth has birthed nothing but intense fragility and hyper-submission to other's opinions. (And at least one of those extended family members died in a most slow and agonizingly horrible way possible as it became clear mid life his life was.. well... a bit messy)
You can see a sort of paralell in Mordin, he ultimately ends up basically having to sacrifice himself to solve his own problems. That is not a hero, that is a screw up who is nonetheless at least partially capable of seeing and responding to his own screw-upness. A person doesn't really get credit for solving problems they created in the first place. At best, they do solve their own problems in a way, at worst they try and force the world or others to view their state of fragility as heroic and powerful, and which, predictably, leads to even more problems.
The reality is that we don't really have a choice about facing thorny moral questions, we all must simply answer them as best we can. If one cannot give their own answer, then a default or someone else's answer will be given, and the default, much like the default result in other areas of the universe, is usually not all that good.
Hm well that got quite long, I guess I didn't need the pizza so badly... definitely going to need that or soda or something soon though.
Well one more thing, to get it back to the topic. As I was saying, Tali demonstrates that sublime control tendencies and humanity are not mutually exclusive. The Quarian's relationship with the geth is a symbiotic and mutually beneficial relationship, even though obviously it is far from perfect. Rather than haplessly become a scientist as part of a geth extermination battalion, she is devoted in heart and mind to the process of relating to and grasping with the essence of the problem on her own terms. Consequently, she is better able to formulate her own opinion and stance in contrast to the others who would push and prod her into more extremist ideologies (various Quarian admirals, commanders, leaders, etc)
She was, to again use an analogy, Marie Curie, someone who did not let her place of birth or original understanding of self cloud her ability to assess and interpret outside information, which in her particular case meant becoming more familiar with the country of Poland and her relationships with it, and which enhanced and aided her sympathies and understandings of, the outbreak of WWI.
Arguably, putting aside the issue of the atomic bomb entirely, she was just a much better scientist too while we're at it, Oppenheimer was fast and productive but he was also very derivative in almost every aspect of his work, whereas Curie ran successfully rough-shod over established doctrine at nearly every turn.
It's not as though Tali and Mordin are even chasms apart though either, necessarily, (although at least one big chasm for sure) it's simply that she has the presence of mind to define her own framework and ability to solve issues, and whatever her ability is in that respect, she is entitled to precisely that level of greater self-power.
Kay soda or something now soon good grapes, I just got going there I guess.