It starts small and insignificant barely even noticeable but that is the seed which will spread. Some things simply can not be contained and merely being around them can infect you. It's a subtle process that progresses over time. It's not as though you're rapidly consumed and somehow remain the same on the inside just waiting to break free. The truth is that corruption is complete in that it's not just a part of you eventually it is you. It works from the inside out so that it is almost entirely undetectable until it's too late.
There's more than one type of corruption though and not all of it is inherently bad. To reiterate though corruption comes from the inside, it's not something that can be truly forced on you. While some people may look corrupt or are forced in to situations a corrupt person would gladly accept that does not mean that they are in fact corrupt. For example corruption through subversion in which we manipulate existing corruption in a system for good is not a corruption of ourselves or if it is then it is equally balanced in opposite so that it may not gain. Receiving something for doing anything which you're already obligated to do for some reason or another is by definition corruption of some kind, yet it may be that you need what you are receiving and thus accepting it in return for nothing could be justified. The same would go if you were to use the above example inverse so that you are giving something to someone for what they already do with a byproduct to the benefit of someone else.
There are those who would say a little corruption can be good. The problem with that is even a little corruption leads to more substantial corruption without fail. It may start as a doctor seeing a patient early for a few extra dollars, yet it may end up as him manipulating organ donation systems for patient preference. Though perhaps in opposition corruption leads to generation. That is to say a deviation from ideal views may lead to a new acceptance in which what is correct may change. All of science was once viewed as a corruption of thought and now it's accepted as truth. The question then becomes are the consequences worth the gain which is indeterminate until it has been created as a byproduct. The answer to which I would say is likely to be no as the byproduct could be obtained through other less detrimental methods aside from the fact that the gain is less than the loss for a substantial period of time, and of which the consequences and effects could likely be observed and shown to have been a reduction in accelerated progress for which we may never recover. For example where would we be if the dark ages hadn't happened? From a science standpoint we can clearly see the loss and repression and how far we've come and at what rate which suggestively would have happened much sooner without the dark ages leaving a gap where we should be.
Thus corruption even under noble cause should be fought at every opportunity for the benefit of the world. Though sadly this will not happen and in the case of the world today that is probably to the benefit of it's people. If we suddenly ended all corruption today I'd be unsure if we would live beyond tomorrow.