The range plays important factor in how much damage your shots deal. At distances between 30 and 60 meters meters, points spent in range perks of weapons give out higher damage bonus than points spent for base damage would (i.e. longshot works better than master commando). Silencers negatively influence the range parameters of your weapons, hence they influence the damage you deal at longer ranges.
Silencers also override projectile type. The issue with that is that legendary system is inconsistent, and each legendary effect should be considered separately for each projectile type. This is a fluid matter, but silencers have been previously negating various legendary effects, raising lots of "this effect doesn't work" reports that attributed the issue to effects themselves, when removing silencers fixed the issues. An example: 50% crit damage legendary effect provided no advantage (only in PvP) when comparing 1* weapon with 2* weapon with same prefixes, when the weapons were silenced. Upon removing silencers, the one with crit damage bonus provided significantly higher damage output.
If you really have a need for a silenced weapon, make it your side weapon, preferably one that's using other ammunition that your main. Fixer modded to .38 works magnificent for this purpose.