You say chemtrails are implausible? We already know that the TLA's have experimented with mind control agents, ala MKULTRA (though under different circumstances) and probably other still-secret programs, so using the rubric you just described, chemtrails are also a legitimate fear.
Not really. Think of it in terms of the number of assumptions necessary for each scenario to be true. For the case of spying, the only assumption necessary is that there will eventually be a confluence of opportunity for malfeasance and someone inclined towards unethical behavior. What is the probability that these two events occur simultaneously eventually? Very high indeed. A highly plausible scenario would be simply an analyst looking up information against a political candidate they don't like and leaking personal information they find to sink a campaign. The fact that analysts have spied on romantic interests shows that opportunity and disposition has already occurred. The plausible scenarios only get more sinister from there.
When it comes to chemtrails, a whole string of highly improbable assumptions are necessary for it to be true. The probability of these two cases are not comparable.
You say chemtrails are implausible? We already know that the TLA's have experimented with mind control agents, ala MKULTRA (though under different circumstances) and probably other still-secret programs, so using the rubric you just described, chemtrails are also a legitimate fear.