Hmmm, let's see.
- Pouring acid over a sentinent being, which was perfectly contained an no threat at the moment (partially a fault of game design since the only other option is to free it)
- Constantly making xenophobic remarks, even though half your crew consists of aliens (not evil, but still a hilariously d*ck move).
- Slaughtering a whole village full of mind controlled people just because you are to lazy to use the non-lethal munition you have avaiable.
- Shooting a prisoner that surrendered (without fight no less) and willingly gave you all the information you wanted in the face because...... no real reason really.
- After finding out that Cerberus horifically tortured an autistic teenager for some already morally ambigious experiment, leave said teenager in Cerberus' care.
- Kill Samara in order to replace her with her (at best) equally strong daughter, who happens to me an unapologetic serial murderer with a literal addiction to killing people, which even promts her to try kill you after the collector base.
- Saving a woman out from an exploding building, allow her mother to commit suicide, and then shoot her in the face.... just because... It wouldn't have been personal enough to let her die in the explosion I guess.
Yes truly, these are all actions of pure pragmatism. In no way are any of these completely needlessly cruel or even downright detrimential to you (*cough* Morinth *cough*). Renegade Shepard is truly a shining hero of logical thinking and getting priorities right if s/he makes these choices and in now way is s/he an unhinged sociopath for pulling of this kind of cr*p. 
1. Eliminating the rachni queen is a solid, pragmatic choice. Balance the detailed knowledge of the Rachni Wars vs. talking to it for 5 minutes. It will say anything to save itself.
2. Not evil, just a dick move as you say.
3. What guarantee do you have that it will work? Shepard doesn't know the nature of the contagion yet, the choice to kill them can be justified. (never did that myself, just spitballin')
4. Which prisoner? Rana Thanoptis? Plenty of reason to think she was indoctrinated and guess what! She was!
5. If you accept that the Geth are a mortal threat to civilization and that David is un-salvageable, then it becomes a regrettable necessity to continue the project.
6. Yeah, that's just dumb. Only ever did it to unlock dominate then reload.
There should be an option to waste them both.
7. Can't blame the player for cutscenes taking away their agency. It's quite possible that a) Samara has directly threatened you and
no matter what she says, why trust an Ardot-Yakshi? Better safe than sorry. Personally I would have nuked the site from orbit afterwards to clean up any other possible stragglers.
Alternatively, if you must insist Ren-Shep is evil, I give you The Operative
https://www.youtube....h?v=YeT7MzDcpeg
Since we don't know if Shep actually does survive high EMS destroy, she doesn't get to live in the better world she fought for.
(I could sworn we had an embed video button on this forum, too lazy to do it manually)