It's not totally unreasonable that they choose to charge more for their service. They've gone 8 years without raising the price.
What is unreasonable is that they chose to charge for it in the first place, XBL isen't doing anything that others haven't been doing free og charge for ages.
They even tried to do this for the PC, at it's inception GFWL would require a gold account to play online, but they had to scrub that, because PC gamers where not about to pay for something they got for free elsewhere, and had gotten for free since the start of online gameing, but ofcourse, Xbox owners have no alternative if they want to play their Xbox online so they gotta pay.
Personally, i don't understand why the Xbox 360 became so popular, it's been plagued by faulty hardware since day 1, MS tries to charge you for everything you do (from playing online, and all the way down to "custom avatars" and the like), and it's nothing special, it's not like it's leaps and bounds ahead of the PS3, infact the two systems are quite equally matched.
I guess what it all comes down to, is that MS where more succesfull at bribing publishers and developers to favour their platform, more exclusives, earlier releases, better marketing, more "lead platform" status, all that shady stuff, and people, beeing suckers, fell for it en masse.