Speaking as a former IRC op.
As productive as IRC can be for the well-mannered person, it's also the sort of place that tends to collect people with poor self-control. Younger people, the disaffected, mentally unbalanced, etc. When angered by some real or imagined slight, these folks tend to love launching DOS or DDOS attacks against the IRC servers and/or those IRC clients whose IP address is visible via a /WHOIS command.
A person determined to be a nuisance to your IRC server will continue being a nuisance for as long as he/she wishes. Many proxy lists are available to the determined nuisance; blocking/banning by IP address thus becomes a constant manual hassle. There's no sure way to automate it; these skript kiddies can and do vary their scripted or manual attacks quite often. Longterm the only way to win is to have a team of people who thus have a longer attention span than the average angry teenager.
An IRC server of any popularity at all is nearly guaranteed one or more such attacks per month; dealing with these attacks requires time, expertise, and tools that many low-cost hosting providers just don't have available and don't see any profit in acquiring.
I stay on IRC a fair amount of the time, via irssi/screen running at Silence Is Defeat (SiD). It costs a buck to signup, and there are no recurring costs. But the quality of service has been going downhill lately; the SiD server is often a tad overloaded and thus can lag a few seconds at times. So you might check out a few other free shell providers. If all you need is an irssi/screen host and the occasional ping/traceroute/nmap, you'll soon find one that works well for you.
rsync your homedir to your local machine every so often though; of course being free, you're not exactly gonna get an ironclad SLA!