Normal games don't matter I guess, having a smurf, well, at least you don't lose LP? You can still have fun, and I play normal games to relax and don't care about the outcome at all.
About the ranked games, if you are iron - gold, having a smurf in your opponent team will trigger you, and if you think positive, you will say ''i could be this guy''. You'll watch replay or just kills and notice why is he better and what has he done better than you. At least I did that, I was bronze before, last season I ended up plat 2 (not high elo, but I'm fine with it). I never had problems with smurfs, the real smurfs, good players, they will never be toxic, because they know they are not matched up against their elo, and are there to help a friend climb or just made another account, you can ask these guys for tips. There are other smurfs aswell, baby smurfs I like to call them. They aren't high elo, but high enough to carry games in bronze/silver, like plat, I can carry games till gold 4 without a problem. The thing is, they are toxic because they are frustrated for not being able to climb anymore in their elo, so they just want to feel the joy of winning a game, stomping someone and having a high score. You just ignore those, because they don't climb anymore, they reached their max elo. Just focus on realizing your mistakes and turn that ''having a smurf'' into having an opportunity to play vs a good player and realize why is he better than you, at least for now ;) Hope I motivated you because I've experienced it myself, I don't smurf and even when I do play on a lower elo account, I don't feel above anyone when I win because I know I'm not matched up against my elo.