Depends who you ask. Milton Friedman argued that capitalism cannot be seperated from freedom as
"[e]conomic arrangements play a dual role in the promotion of a free society. On the one hand, freedom in economic arrangements is itself a component of freedom broadly understood, so economic freedom is an end in itself. In the second place, economic freedom is also an indispensable means toward the achievement of political freedom." [1]
On the other hand, Karl Marx saw capitalism as dividing society into the haves and have nots - the haves being the bourgouise with all the wealth, and the have nots being the proleteriat who had none of the wealth. Marx, obviously, was not a fan.
The XKCD strip is about whether or not it's a good thing to have tech companies with overwhelming amounts of power in certain areas. That's orthogonal to whether or not such behavior is strictly legal.
