The fact that it can be used to "justify" almost anything. It obviously doesn't work as a defense in the court, and neither does it work as a justification for doing legal but unethical things.

If you want a consequentialist answer:

If, for ethical reasons, fewer people were willing to take these jobs, then either salaries would have to rise or the work would be done less effectively.

If salaries rise, the business becomes more expensive and harder to scale. If effectiveness drops, the systems are less capable of extracting/using people’s data.

Either way, refusing these jobs imposes real friction on the surveillance model.

If you want a deontological answer:

You have a responsibility not to participate in unethical behavior, even if someone else would.