Hi,
Only traffic explicitly permitted should be allowed to pass through the firewall, there is always an implicit deny at the end of an ASA access list for the traffic that hasn't been permitted.
You need an ACL to pass traffic from a lower (outside) security level to a higher (inside) security level, it is denied by default. You would create the ACL and then permit only the traffic you want - the implicit deny rule would always be the last rule processed, you don't need to define it, otherwise that would be an explicit deny.
You can't technically remove an implicit deny, all you can do is define a permit ip any any rule which would permit all traffic, that's not what you want to do, especially if it's a perimeter firewall protecting the local network from the internet.
HTH
