Full nodes derive their security from enforcing all of the rules of Bitcoin self-sufficiently on any data they receive, and by validating the complete blockchain from the genesis block to the chain tip. This does not require keeping the data after validating it. Pruning nodes have the same security that archival nodes have. Since following Bitcoin's rules is sufficient to converge to the chain-tip, pruning nodes have full consensus capability.
The only difference is that pruning nodes cannot serve the blocks that they have pruned, and if a pruning node requires a
-reindex for any reason, it will need to repeat the full Initial Block Download (IBD).