Compare Japan -- its wealth, living standard, etc. -- with any former colony of any empire, including Japan's own. It seems clear to me that getting colonized by a capitalist empire is not a good deal compared to not getting colonized by one. It shouldn't take a Marxist to understand that.
[WS:] I am glad that you mentioned Japan. It developed during the Meji Restoration, which was wholesale copying of Western organizational forms (cartels) and technologies. Cross national "borrowing" of Western institutions and technologies was by far the main form of influence.
However, even directly colonized countries benefited, on balance. East African states are carbon copies of British institutions, for example. India is a more complicated case, but Marx made a compelling argument about the positive effects of the British rule there.
Even if you factor in the atrocities committed by Western powers in colonized countries, you need to look into NET EFFECTS of such atrocities - i..e. the difference between atrocities already perpetrated by local tyrants, slave traders, non-westerners (e.g. Arabs in sub-Saharan Africa) and those committed by Western powers. In many cases that net effect was negative, that is, westerners actually reduced the atrocities (cf. the British role in stopping the slave trade practiced by Arabs in East Africa.)
So the bottom line is that if factor in cross-national "borrowing" and net-out the amount of violence already endemic to the "third world" regions - the Western influence looks quite positive on the balance. Of course, that does not mean that any atrocities committed there are justifiable, but that is another story.
On a lighter side, consider the following excerpt from Monty Python's "Life of Brian"
Scene 9
FRANCIS: We're gettin' in through the underground heating system here, up through into the main audience chamber here, and Pilate's wife's bedroom is here. Having grabbed his wife, we inform Pilate that she is in our custody and forthwith issue our demands. Any questions?
COMMANDO XERXES: What exactly are the demands?
REG: We're giving Pilate two days to dismantle the entire apparatus of the Roman Imperialist State, and if he doesn't agree immediately, we execute her.
MATTHIAS: Cut her head off?
FRANCIS: Cut all her bits off. Send 'em back on the hour every hour. Show them we're not to be trifled with.
REG: And of course, we point out that they bear full responsibility when we chop her up, and that we shall not submit to blackmail!
COMMANDOS: No blackmail!
REG: They've bled us white, the bastards. They've taken everything we had, and not just from us, from our fathers, and from our fathers' fathers.
LORETTA: And from our fathers' fathers' fathers.
REG: Yeah.
LORETTA: And from our fathers' fathers' fathers' fathers.
REG: Yeah. All right, Stan. Don't labour the point. And what have they ever given us in return?!
XERXES: The aquaduct?
REG: What?
XERXES: The aquaduct
REG: Oh. Yeah, yeah. They did give us that. Uh, that's true. Yeah.
COMMANDO #3: And the sanitation.
LORETTA: Oh, yeah, the sanitation, Reg. Remember what the city used to be like?
REG: Yeah. All right. I'll grant you the aqueduct and the sanitation are two things that the Romans have done.
MATTHIAS: And the roads.
REG: Well, yeah. Obviously the roads. I mean, the roads go without saying, don't they? But apart from the sanitation, the aqueduct, and the roads--
COMMANDO: Irrigation.
XERXES: Medicine.
COMMANDOS: Huh? Heh? Huh...
COMMANDO #2: Education.
COMMANDOS: Ohh...
REG: Yeah, yeah. All right. Fair enough.
COMMANDO #1: And the wine.
COMMANDOS: Oh, yes. Yeah...
FRANCIS: Yeah. Yeah, that's something we'd really miss, Reg, if the Romans left. Huh.
COMMANDO: Public baths.
LORETTA: And it's safe to walk in the streets at night now, Reg.
FRANCIS: Yeah, they certainly know how to keep order. Let's face it. They're the only ones who could in a place like this.
COMMANDOS: Hehh, heh. Heh heh heh heh heh heh heh.
REG: All right, but apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, a fresh water system, and public health, what have the Romans ever done for us?
XERXES: Brought peace.
REG: Oh. Peace? Shut up!
[bam bam bam bam bam bam bam]