Invest or Hold?
It's a fairly interesting question - but the answer entirely depends on how and why you got into crypto in the first place.
My advice to anyone invested in any asset class that's even half as speculative as the Cryptocurrency market is; Why are you trying to realise a loss?
If you followed basic investment advice, you would have only invested an amount you didn't really care about. Therefore, if that amount has lost 30, 40 or even 60% of it's value - why do you give a shit?
The only reason you are thinking to sell is because you didn't listen to basic investment advice and you threw more money than you could afford into Crypto. This would be silly, and no, there is not a reasonable excuse in "I believe in the Blockchain Technology". In fact, if that is anybodies excuse for investing in Crypto I would argue that they don't understand the BC technology or Crypto enough to be investing in the first place.
Cryptocurrency is a tiny, fairly boring, part of the tech - the tech itself is more about a new way of thinking about "the third party" and trust between two individuals.