Because while it may result in a stable, positive, loving relationship (or just mutually great, harmless sex that’s what they’re after), it’s a strong predictor when people are actively seeking a relationship with that kind of gap. Think about the likely reasons someone would seek that kind of thing, and the likely outcomes. I think it’s reasonable to look at this sort of thing with suspicion, but not to immediately dust off the pitchforks and light the torches.
Not all middle-aged single men distributing candy from the back of their windows van are paedophiles, but it’s both reasonable and responsible to look at what they’re doing with suspicion.
It’s interesting you’d bring politics into this when conservatives seem so wrapped up in protecting child brides, child beauty pageants, fetishise youth, and appear to be massively over-represented represented in paedophilia stats.