I wrote about this in a previous year but got rid of the post in a blog shuffle -- but now I'm making the point again: seedless watermelons are an abomination.
In the first place, they lack the slightly chewy grainy texture of really red, black-seeded watermelons. Secondly, they lack the intense exquisite succulent sweetness (they may have the succulence, but that's all). Thirdly, the triploid 'seedless' mutant watermelons lack the deep inviting pinkish red of real (viable, diploid-DNA) watermelons. They are not the colour red so much as the colour of defective gums. Call them 'gingivitis watermelons' ... yum.
Unfortunately, it's been a few years since I've had the delight of a genuine watermelon. Apparently this is because of consumer demand, but I wonder. Keep giving people this poor substitute, and pretty soon they'll forget the real thing tastes like. Well, I haven't forgotten. If this goes on, the only thing I'll ever use watermelon for is infused water -- the flavour defectiveness matters less when the slight tang is actually a blessing in a cold glass of water. But I certainly won't buy watermelons for eating. In fact I probably won't buy them at all.
The fact is that black seeds -- reproductively useful seeds -- are part of the hormonal maturity of the fruit that gives it its distinctive colour and its wonderful flavour.