Most people who take Viagra have hypertension, because hypertension is the main cause of ED. That doesn’t mean Viagra is dangerous, but you shouldn’t combine it with certain other drugs.
There is a world of difference between valproate and Viagra. Valproate causes birth defects and cognitive delay in 30-50% of pregnancies, which is astonishingly high. If Viagra caused permanent harm to even 5% of users, it would already be off the market.