Gross misuse of the word 'illegal' going on here.
No 'Laws' are being broken. Google's webmaster guidelines do not get enforced in court. You will not go to prison, nor will you get a fine. Unless your playing a game of Google Bowling and wiping out your competitors, its all good.
My personal stance; Its not my job to write Google's algorithm, and it certainly isn't job to make a huge multinational conglomerates life easier. Who they put that the top of the SERPS is completely up to them, as is how they determine that. I'm not employed by Google. I don't get a say.
As an SEO, my job is to second guess them, and to bring paying customers onto websites as a result. If Google has written an algorithm that ranks sites that buy links...whelp. Their bad.
But, that said, Google has made their intentions clear that they want to filter this behavior out. They'll either figure out how, or they'll die on their arse and we'll all start searching on Facebook or something.
Either way, Link purchasing isn't a long term marketing strategy. And most legitimate business' want long term marketing strategies. White-Hat will probably continue to pay dividends years from now.
Its not morals. I couldn't give any less of a crap what Google thinks of my activities. Its what's best for the project. And what's best for the project is rarely just throwing money at the problem.