If you haven't, read some more biographies about the man. You'll discover that things were a bit more complicated than what you may currently believe; above all else, Edison was a businessman who invented, and an inventor who knew business, and saw opportunities where others didn't.
That doesn't mean he was a saint - he had and did plenty of things that on retrospect weren't very moral, and questionably illegal. The way he treated his wife and children was terrible - but wasn't out of the norm for the era (unfortunately). And he was a master of taking and expanding on other's ideas and marketing them as his own; you can call that theft - perhaps plagiarism is a better term? - but it isn't anything different than what still happens today.
Excusable? No - but again, it's more complex - and Tesla had his own faults. I've found in my reading about both men, that they were both complex characters of their time. The real tragedy, IMHO, is that their individual prides got in the way of the possibility of their mutual cooperation; had they done so, history would likely be much different today.