Struggling with Negativity

I listened to Podcast 155 on Negativity and am having a hard time embracing the whole idea of “Nothing is negative—only your thoughts about it make it negative.” When it’s something minor, such as a co-worker making a sarcastic comment, it’s easier to shrug it off and make it not about you so that it doesn’t stir up negative feelings. But if it’s about something more serious, such as murder (to use an extreme example), how can it be thought of as neutral? Making a thought statement of, “He murdered his wife, and that’s ok.” just does not seem right. Some things may be subject to how we perceive and think about them (i.e. politics, opinions of others), but other things definitely can be defined as bad/evil.
I also noticed that it is easier to switch to a positive thought about a situation when I am in a good mood, but when there are circumstances that (based on my thoughts) are challenging—such as my husband getting laid off, it is much more difficult to do the switch. If I keep pushing myself to come up with positive thoughts, it feels very superficial and Polyanna-ish. It feels very inauthentic and a bit like being in denial. Please explain this piece on Negativity, so I can embrace it better.