Yeah, the Mystics talk about Magus creating/summoning Lavos because they thought that he was going to somehow use Lavos as a weapon against the humans in their war. Either he told them that or he let them assume that when he told them what he was planning...either way it comes to the same...
How would you feel if you just lost your closest friend and got turned into a frog at the age 0f 16/17?
You use this as an excuse for Glenn's cowardice, and yet the same thing happens to Janus and it's...
A ruined life? How does losing your sister ruin your life? Sure, the guy had a rough time, but I've seen worse.
Janus was fatherless, watched his mother go insane, was already ostracized within Zeal for not having Magical abilities (presumed a bastard because of this by one translation as I recall), his only friends were his big sister Schala and his little kitten, Alfador...and then Lavos goes and takes THAT little bit of happiness from him...along with all semblance of his regular life. And Janus was MUCH younger than Glenn when Cyrus died...though I don't know if I'd say Glenn was 16/17...but that's debatable as it's not confirmable either way in-game...
Magus is just a go-getter. He has goals and nothing will stop him from achieving them or at least attempting them. Also, I've always been one to say that he tries to use the Red Knife/newly formed Masamune against Lavos (it shows him use a red weapon, anyways), thinking it would be a weakness...thus prompting him to say, "What? It didn't work?" when his blow against Lavos fails to cause it any undue distress. If his goal is the destruction of Lavos for taking away his world, is that really much different than Crono & Co.? They're just doing it for the future of the world being taken away where Magus is doing it for the past world that was taken away. If anything, he has MORE reason to go after Lavos as it affected him directly (let's have no Magus=teh Entity discussions though, shall we?).
Also, sure, Crono & Co., whom he was completely unprepared for having not had to deal with other humans capable of wielding Magic at all, defeated Magus
3-on-1, and they had a better version of the Masamune, all while he was being controlled by the CPU. In a true 1-on-1 with Magus & Frog, the green guy doesn't have much of an actual chance. Water Magic Barrier+Dark Matter=1 dead Frog. Maybe he'd get lucky if he got a Frog Squash in before he bit it...but w/e...doubtful...especially since Frog didn't/wouldn't know that ability at that time.
Do we
know that
Magus has killed innocents? MAYBE indirectly, but...ARE there even innocents in WAR? Again, on translation, I recall, suggests that it was the HUMANS who were, in fact, originally encroaching on Mystic territory (which would certainly explain what Ozzie was doing in the mountains behind Truce...and why Mystics are STILL there in 600AD)...
The only pure person in entire Zeal was probably Schala.
I'm not entirely sure what you mean when you say 'pure' here...but what about the Gurus? Plus, Janus was just a KID...cut him some slack...how would you turn out w/a schizo mother & no dad? Not to mention everyone was being influenced by the power of Lavos, emanating from the Mammon Machine...