It might depend how many parasites vs how many symbiotic relationships you have. Parasites are quite easy to acquire and harder to shake off, and often have powerful institutions on their side like courts and police or gangs or economic power.
Conversely it's quite easy to accidentally fuck up a symbiotic relationship. Or for a relationship to degenerate due to any wavering trust level.

If someone suddenly stopped talking to me because I was being a dick I’d at least hope i have enough self-awareness to put the blame on myself. People don’t have to put up with unreasonable levels of dick-ish behaviour. They should have a way out. The pity for the suicide ones is that they couldn't find a better way out.

I'm highly sceptical of those calling it selfish; were they really in a give and take relationship, or were they taking more than they gave - only they know that of course. Though I suspect people often lie to themselves about such things.

Conversely if some of the worlds major parasites suddenly committed suicide then I might call that a rare moment of selflessness.