Though open, this is a fantastic question, and one that everyone who is not a climate scientist should ask. The answer inevitably will vary depending on what you are willing to take people's word for, and how much time you're willing to spend digesting enough evidence to be convinced one way or another.

As shorthand in the following I will say that everyone, on this issue, can be classified as an "agnostic", an "alarmist", or a "denier", and I will trust you not to take those labels to insinuate anything about who is right or wrong (I myself am mostly in the alarmist camp).

IMO, the alarmists win A LOT of points (maybe not quite the whole game) for having a coherent, universally accepted, physics-based theory of the temperature of planets which correctly predicts observations from a variety of planets and requires radiative forcing from greenhouse gases in order to do it, while the deniers (as far as I can tell) do not propose an alternative theory or even generally agree on which part of the alarmists' chain of inference is broken. In, fact, until I see such a theory presented by the deniers (why are the planets we know the temperatures that they are, and what is the relationship between those temperatures and atmospheric GHG concentrations?), I really think the only sane stances to take are that of the alarmist or that of the agnostic.

Now, if you doubt that people can agree on the current surface temperatures and atmospheric compositions of Venus, Earth, the moon, and Mars, and are unwilling to spend the time to convince yourself that they do, then you're likely doomed to agnosticism. Same deal if you doubt that we can agree on the amount of CO2 we're emitting as a species on an annual basis.

Even then, you'll have to remain agnostic unless (1) you're willing to accept an appeal to authority or (2) you're willing to spend tens (but probably not hundreds) of hours understanding the basic theory of ACC, which holds that a doubling of the earth's CO2 concentration will result in an increase of 3C (plus or minus 1.5C) in the Earth's equilibrium temperature.

If you want to spend those tens of hours, you could start with this article[1] or this video lecture[2] or the wikipedia articles on "Planetary Equilibrium Temperature", "Radiative Forcing", and "Climate Sensitivity". The trick to not spending more than tens of hours is to remain laser-focused on understanding what those three terms mean, how they're related, and how one can try to measure climate sensitivity. In particular, a lot of discussions about prehistoric climate, on feedback mechanisms, and on the specific effects of global warming on specific regions of the globe will lead you astray if you let them.

If you don't have even a few hours to dig in on climate science, all I can say is that appeals to authority become a lot less unpalatable when the authorities appealed to are sufficiently numerous. Even if you think it not unlikely that NASA, NOAA, the EPA (all of whom are definitively, officially in the alarmist camp according to their websites) are in conspiracy with faculty at dozens or hundreds of universities, what about the 197 nations that were engaged in negotiating the recent Paris Climate Accord, or the 84 signatories of the Kyoto Protocol?

Lastly, just out of curiosity, in what form do you tend to see the genetic fallacy applied for or against ACC? I'm not sure I've encountered it.