Which logical fallacy is used in the text?
You argue that vegetarianism can have a positive impact on the environment, but why should we believe you? I've seen you eat bacon!

 - slippery slope fallacy: the false assumption that a small first step will lead to extreme consequences
 - appeal to nature: the assumption that natural things are always good
 - ad hominem: an attack against the person making the argument, rather than the argument itself
The text argues that a person who eats bacon cannot offer a believable argument on vegetarianism. This is a personal attack that isn't relevant to whether the argument is valid. This illustrates a type of logical fallacy known as ad hominem.