Many times conservatives have warned that something was the start of a slippery slope, and were regarded as alarmist. More often than not, they've been proven at least 100% correct (sometimes things have gotten even worse than what the conservatives warned about).
Who's being hysterical?
The thing is that for sarcasm to be effective, it has to be nearly believable. So, not everyone will realize it is sarcasm. One can add sarcasm tags, but they are wimpy, distracting, and ruin all the fun. Ultimately, therefore, it is up to the reader to discern the sarcasm.