Building too many links to your pages will NOT harm your ranking in any way.
If it could, everyone would be signing up for those mass spammy link services for their competitions sites in an attempt to "sandbox" them.
The fact is there is nothing your competition can do to harm your rankings.
If you need a reference from Google to prove this, please see: Can competitors harm ranking? - Webmaster Tools Help
"There's almost nothing a competitor can do to harm your ranking or have your site removed from our index. If you're concerned about another site linking to yours, we suggest contacting the webmaster of the site in question. Google aggregates and organizes information published on the web; we don't control the content of these pages."
This would suggest that buying mass links can never hurt your rankings, but then again, it won't help a whole lot either. Google often discounts the values of your backlinks if it notices an unnatural pattern (ie; 20K profile links in 24hrs probably won't move you to number one spot )
Always create links ethically and focus on quality. There is nothing bad about using automated tools to speed the process up, just use them properly and don't overuse.