Viserys has never been shown to view himself as a paragon. Where are you getting that from, dude?
Plenty of people do things that make them feel guilty, some good, some bad, and some quite atrocious. There is nothing wrong with acknowledging that guilt, mulling over it in your head, reflecting on what lead you to commit such actions, etc., but they don't all collapse into snivelling sacks of self-loathing and angsty goth poetry.
So what if Viserys felt guilty in this instance? It was justifiable, given his personality and the manner in which he experienced the deaths of those children. He didn't read a report about it, or receive word from a subordinate. Instead he got to relive the entire experience in 3D surround sound high definition virtual reality with smellovision thrown into the mix. That's incredibly visceral and not something you can simply ignore without having something genuinely wrong with you. I freely admit I probably have a screw or two loose in this instance, because I doubt it would bother me overly much, but at least I can acknowledge that it should cause a reaction.